JPH11183329A - Life inspecting device and inspecting method for dynamic pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict the life of a dynamic pressure bearing device at the time of shipping. SOLUTION: The contact between rotary members 22, 23 and fixed members 12, 16 in the rotation stop process detected with an acoustic piezoelectric element 3 in response to the fitting level, for example. The fitting level is satisfactorily detected based on the detected result, thereby the device life is predicted.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which a dynamic pressure is generated in a lubricating fluid, and the rotating member is axially supported with respect to a fixed member by the dynamic pressure of the lubricating fluid. The present invention relates to a device and a method for inspecting the life of a hydrodynamic bearing device. 2. Description of the Related Art In recent years, in various devices such as motors, various types of dynamic pressure bearing devices utilizing the dynamic pressure of a lubricating fluid such as oil or air have been studied and proposed so as to cope with high-speed rotation. I have. In this dynamic pressure bearing device, the dynamic pressure surface on the fixed member side and the dynamic pressure surface on the rotating member side are arranged to face each other, and a dynamic pressure generating groove is formed on at least one of the two opposing dynamic pressure surfaces. The lubricating fluid, such as oil or air, interposed between the opposing surfaces of the rotating member and the fixed member is pressurized by the pumping action of the dynamic pressure generating groove during rotation of the rotating member, and the dynamic pressure is increased. Action occurs,
Rotational support is performed such that the rotating member is held in a floating state by the dynamic pressure of the lubricating fluid. The inventor of the present invention has found that in such a hydrodynamic bearing device, the degree of “fit-in” between the fixed member and the rotating member greatly affects the characteristics and life of the hydrodynamic bearing device as described below. And found that it is an important factor that governs the reliability of the device. First, generally,
"Familiar" means that members that are in sliding contact with each other under high pressure conditions are initially worn due to the effects of assembly accuracy, surface roughness, etc., and the surface pressure is reduced due to a smooth contact surface state. However, in the combination of the high hardness member and the low hardness member,
The surface pressure does not decrease until the surface roughness of the high hardness member reaches a predetermined smooth state due to wear. [0004] Considering the phenomenon of "similarity" to a hydrodynamic bearing device, first, at the time of high-speed rotation, a complete oil film is formed on a wedge-shaped portion formed between the fixed member and the rotating member. As a result, a fluid lubrication state is established, and the rotating member is maintained in a floating state. On the contrary,
At the time of start-up stop or low-speed rotation, the oil film in the wedge-shaped portion is broken and transits to the boundary lubrication state. In this boundary lubrication state, mechanical metal contact occurs partially, so that the effect of "fit-in" occurs. Whether or not complete oil film formation is performed depends on the assembly accuracy of the shaft and bearing member constituting the wedge shape described above, and the surface roughness of the dynamic pressure surface is an important factor. Therefore, the quality of the “fit-in” in the dynamic bearing device is determined. Attention should be paid to the fact that the depth of the dynamic pressure generating groove is reduced by the abrasion of the dynamic pressure surface generated in the process of the “fitting-in”, and that the lubricating fluid is deteriorated or damaged by abrasion powder and the like. For example, the life of the device can be predicted by inspecting the degree of “fit-in” between the rotating member and the fixed member. [0006] However, as described above, in the dynamic pressure bearing device, the rotating member is held in a floating state with respect to the fixed member, so that "the familiarity" is obtained in the state of steady rotation. There is no significant change in bearing characteristics regardless of the degree of Therefore, in the various inspection methods and apparatuses that are generally performed in a steady rotation state, a clear detection result cannot be obtained even if an attempt is made to detect the degree of “familiarity”. In some cases, reliability after use may be impaired. SUMMARY OF THE INVENTION It is an object of the present invention to provide a life test and a test method for a hydrodynamic bearing device in which the degree of "fit-in" can be easily and satisfactorily performed. In describing the means for achieving the above object, first, the peculiarity of “fitness” in a dynamic pressure bearing device with respect to a general plain bearing will be described. In general sliding bearings, “fit-in” is an essential process in order to stabilize the various characteristics in the operating rotation range, and as the “fit-in” progresses, the bearing driving force is clearly reduced, and other characteristics are also noticeable. Often seen and improved. On the other hand, in the dynamic pressure bearing device, as described above, the influence of the “fit-in” is negligible because the rotating member floats in a completely fluid lubricated state in the steady rotation region. And seems to be independent of bearing properties and life. However, from the viewpoint of the delicateness peculiar to hydrodynamic bearing devices as follows,
Has a significant effect on the life and reliability of the hydrodynamic bearing device. (1) Viewpoint of Oil Amount When a dynamic pressure bearing device is used as a motor bearing device in a hard disk drive (HDD) used as a peripheral device of a computer or a writing device of a laser printer (LBP). Is a fatal problem if contamination occurs due to oil leakage from the dynamic pressure bearing device. For this reason, a design has been made to use a capillary force or the like to ensure the oil retaining function so as not to cause the bearing oil to scatter, but in this case, the amount of oil that can be retained in the dynamic pressure bearing device If a small amount of abrasion powder is generated and mixed, sludge will be generated, and the physical properties of the lubricating fluid will be reduced, which may cause a failure. This is one of the most common reasons that "smooth-out" occurs naturally in ordinary plain bearings, but must be particularly emphasized in hydrodynamic bearing devices. (2) Viewpoint of Depth of Groove for Generating Dynamic Pressure In the hydrodynamic bearing device, the groove for generating dynamic pressure having a shape such as a herringbone is formed with a depth of several μm, for example. This groove for generating dynamic pressure is generally formed on the soft material side from the viewpoint of processing easiness. Consideration must be given to the reduction in the function of the pressing action of the groove. The progression of “fit-in” continues until the surface of the hard member is smoothed, the surface roughness is improved, and the surface pressure is reduced. When this occurs, the characteristics of the dynamic pressure generating groove deteriorate accordingly. That is, initial wear of several μm, which is not a problem in a general sliding bearing, may be fatal in the dynamic pressure bearing device. (3) In view of the material of the bearing member and the operating environment temperature In the hydrodynamic bearing device, a copper alloy such as phosphor bronze is generally adopted as a bearing material which is easy to obtain processing accuracy.
Such a copper alloy differs from stainless steel (SUS) or the like in that the wear rate is greatly affected by the temperature. That is, since the hydrodynamic bearing device is originally developed for high-speed rotation, it generates a large amount of heat due to viscous loss and the like, and also generates heat from components such as an integrated IC (CPU) arranged around the device, thereby causing a high-temperature environment. Often exposed underneath. For example,
In a hard disk drive (HDD), a specification of 70 ° C. may be set. Considering the heat generation temperature of the hard disk drive (HDD), it is necessary to assume an extremely high temperature as an operating environment of the hydrodynamic bearing device. is there. On the other hand, as shown in FIG. 2, phosphor bronze (C519) used in the above-described dynamic pressure bearing device is used.
1) is compared to stainless steel (SUS430F), etc.
When the temperature on the horizontal axis becomes 70 ° C. or more, the wear rate (μm) on the vertical axis tends to increase sharply. Therefore, in a high-temperature environment as described above, the lubricating fluid and the groove for generating dynamic pressure are often damaged. The cause of the rapid increase in the wear rate of phosphor bronze is unknown, but it is estimated that the thermal properties of the oil component of the lubricating fluid chemically adsorbed on the copper surface are involved, and are common to copper-based metals. It seems to be the nature to do. As described above, it is understood from the relationship between the material of the bearing member and the high-temperature environment that the so-called “fit-in” load in the dynamic pressure bearing device must be reduced. As described above, in the dynamic pressure bearing device, it is extremely important to reduce the "fit-in" load. On the other hand, by accurately grasping the degree of "fit-in", the life of the dynamic pressure bearing device is reduced. Can be estimated. Therefore, in the first aspect of the present invention, a predetermined lubricating fluid is provided in a bearing space defined by a dynamic pressure bearing portion that rotatably supports a rotating member with respect to a fixed member. A dynamic pressure generating groove for generating a dynamic pressure in the lubricating fluid filled in the bearing space is provided on at least one of the opposed dynamic pressure surfaces of the fixed member and the rotating member constituting the dynamic pressure bearing portion, In a life testing device for a dynamic pressure bearing device that supports the rotating member in a floating state with respect to a fixed member based on a dynamic pressure action by a dynamic pressure generating groove, a dynamic pressure is generated during the process in which the rotation of the rotating member naturally stops. Detecting means for detecting the degree of contact between the rotating member and the fixed member during a period from when the rotating member comes into contact with the fixed member to when it stops due to a decrease in the distance, and measures the degree of “fit-in” between the two members. ing. According to the second aspect of the present invention, the detecting means detects the acoustic energy generated by the contact between the rotating member and the fixed member, and measures the strength of the contact between the two members. It consists of an acoustic piezoelectric element. Further, according to the third aspect of the present invention, a predetermined lubricating fluid is provided in a bearing space defined by a dynamic pressure bearing portion which rotatably supports the rotating member with respect to the fixed member. A dynamic pressure generating groove for generating a dynamic pressure in the lubricating fluid filled in the bearing space is provided on at least one of the opposed dynamic pressure surfaces of the fixed member and the rotating member constituting the dynamic pressure bearing portion, In a method for inspecting the life of a dynamic pressure bearing device in which the rotating member is supported in a floating state with respect to a fixed member based on a dynamic pressure action by a dynamic pressure generating groove, in a process of stopping the rotation of the rotating member, By detecting the degree of contact between the rotating member and the fixed member during the period from when the rotating member comes into contact with the fixed member to when it stops due to the decrease, the degree of “fit-in” between the two members is measured, and based on the result, Predict device life Like that. Further, according to the invention described in claim 4, the degree of contact between the rotating member and the fixed member according to claim 3 is detected by detecting the acoustic energy generated by the contact between the rotating member and the fixed member. This is performed using a piezoelectric element, and the strength of contact between the rotating member and the fixed member is measured by the acoustic piezoelectric element. On the other hand, in the invention according to claim 5, the maximum value of the contact strength between the rotating member and the fixed member measured by the acoustic piezoelectric element according to claim 4 and the number of rotations at which the maximum contact strength is obtained are obtained. Then, the degree of “fit-in” is determined based on the number of rotations at which contact is started. According to the first aspect of the present invention, the contact state between the rotating member and the fixed member during the rotation stop process which varies in accordance with the degree of “fit-in” is detected. Based on the result, the degree of “fit-in” is detected well, and the life expectancy of the device can be predicted. Further, according to the second or fourth aspect, the degree of “fit-in” can be easily and reliably detected by the acoustic piezoelectric element. Further, according to the fifth aspect of the present invention, the degree of “fit-in” between the rotating member and the fixed member can be satisfactorily obtained based on the obtained data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a dynamic pressure bearing device according to the present invention is applied to a so-called fixed-end-shaft HDD spindle motor will be described in detail with reference to the drawings. First, the overall structure of the HDD spindle motor shown in FIG. 1 will be described.
The stator assembly 1 includes a stator assembly 1 as a fixed member, and a rotor assembly 2 as a rotating member assembled to the stator assembly 1 from above in the figure. Of these, stator group 1
Has a frame 11 which is screwed to a fixed base side (not shown), and a fixed shaft 12 erected at a substantially central portion of the frame 11 extends upward in the figure. . The tip of the fixed shaft 12 (the upper end in the figure)
Are screwed to a fixed base not shown. An acoustic piezoelectric element (AE; acoustic emission) 3 is attached to the bottom of the frame 11 as detecting means for detecting the degree of contact between the rotating member and the fixed member. This acoustic piezoelectric element 3
The acoustic piezoelectric element 3 is attached so as to detect acoustic energy generated by contact between the rotating member and the fixed member.
The detection signal obtained in (1) is recorded on the digital oscilloscope 4 through a preamplifier and a discriminator (not shown). An example of the detection signal recorded on the digital oscilloscope 4 is shown in FIG.
Details will be described later. Further, a hollow cylindrical support holder 13 is provided substantially at the center of the upper surface of the frame 11, and a stator core 14 is fitted around the outer periphery of the support holder 13. The winding 15 is wound around the salient pole portion. On the other hand, in the rotor set 2, a hub 21 for supporting a predetermined recording medium (not shown) is fixed to an outer peripheral side of a bearing base 22. The hub 21 has a substantially cylindrical body 21a on which a magnetic recording medium such as a magnetic disk is mounted on the outer periphery.
A drive magnet 21c is annularly mounted on the inner peripheral side of a through a back yoke 21b. The drive magnet 21c is disposed close to the outer peripheral end surface of the stator core 14 so as to annularly face the above-described outer peripheral end surface. A center hole formed in the center of the bearing base 22 has a bearing sleeve 2 as a bearing member.
3 is fixed. A pair of bearing projections 23a and 23b are formed on the inner peripheral wall of the bearing sleeve 23 so as to be separated from each other by a predetermined distance in the axial direction.
23b are arranged facing each other so as to be close to the outer peripheral surface of the fixed shaft 12. And each of these bearing projections 2
A pair of radial dynamic pressure bearing portions RBa and RBb are arranged in parallel in the axial direction by a dynamic pressure surface provided on the inner peripheral surfaces of 3a and 23b and a dynamic pressure surface formed on the outer peripheral surface of the fixed shaft 12. It is formed so that. The hub 21 is supported by the pair of radial dynamic pressure bearing portions RBa and RBb so as to be rotatable in the radial direction with respect to the fixed shaft 12. That is, each of the above radial dynamic pressure bearing portions RB
In a and RBb, the dynamic pressure surface on the bearing sleeve 23 side and the dynamic pressure surface on the fixed shaft 12 side are circumferentially opposed via a small gap of several μm, and are separated by a predetermined distance in the axial direction. A bearing space formed by a set of narrow gaps is formed so as to be continuous, and the two bearing spaces are filled with a predetermined lubricating fluid such as oil or magnetic fluid so as to be continuous. At least a pair of radial dynamic pressure generating grooves (not shown) in the form of a herringbone are formed in the dynamic pressure surface on the bearing sleeve 23 side so as to be annularly parallel to each other. During the rotation of the lubricating fluid, the lubricating fluid is pressurized by the pumping action of the two radial dynamic pressure generating grooves to generate dynamic pressure, and the dynamic pressure generated by the lubricating fluid causes the hub 21 to be axially supported in the radial direction. Is configured. At this time, the fixed shaft 12 in this embodiment is
Are members having high hardness, for example, stainless steel (SU
It is formed from a steel material that is a chromium-containing alloy steel such as S430F). The surface roughness of the dynamic pressure surface of the fixed shaft 12 as the high hardness member is formed so as to have an average value of 0.5 μm or less with respect to the surface roughness Rp (center line peak height), as described below. Wear of the bearing sleeve 23 made of a low-hardness member is minimized,
It is configured to be as close as possible to the state where the “fit-in” action is completed. On the other hand, the bearing sleeve 23
A material having a lower hardness than the fixed shaft 12, for example, C
u (copper), Cu-Al alloy (such as aluminum bronze),
Cu-Sn alloy (bronze), Cu-Sn-P alloy (phosphor bronze, etc.), Cu-Si-Sn alloy (silicon bronze), C
u-Ni-Zn (such as nickel silver), Cu-Ni-Fe alloy (such as copper), Cu-Be alloy (such as beryllium copper), C
Copper such as a u-Zn-based alloy (such as bronze) or copper-based alloy copper is employed, and the above-mentioned groove for radial dynamic pressure generation is easily formed on the bearing sleeve 23 made of this low hardness member. Have been. The surface roughness of the dynamic pressure surface of the bearing sleeve 23 made of this low hardness member is such that the surface roughness Rp (center line peak height) of the fixed shaft 1 made of the above-described hard material is high.
The surface depth is set to be at least twice (1 μm) larger than the surface roughness (0.5 μm) of No. 2 and the depth of the groove for generating dynamic pressure can be increased even if the abrasion by the fixed shaft 12 made of a high-hardness material progresses slightly. It is configured to be maintained at a predetermined amount or more. On the other hand, as the lubricating fluid in the present embodiment, trimethylolpropane (TMP) or pentaerythritol (PE) and carbon atoms having 5 carbon atoms are used so that the life of the lubricating fluid and good bearing characteristics are compatible. And oils having a structure in which the fatty acid is esterified with a linear or branched fatty acid having an evaporating rate of 10 ^-7 g.
/ H · cm ² (at 40 ° C) or less and viscosity is 30 cP (at
Oil below 40 ° C) is used. When injecting such a lubricating fluid into the interior of the bearing, the assembled motor is once put into a vacuum chamber, and the vacuum is applied to the motor using capillary force or external atmospheric pressure. This makes it possible to fill the entire bearing interior with the lubricating fluid in a state where the air content is low. As described above, the bearing space constituting a pair of adjacent radial dynamic pressure bearing portions RBa, RBb is formed to extend continuously in the axial direction. An oil reservoir 30 formed of an enlarged space in which the bearing sleeve 23 is depressed outward in the radial direction is formed between the bearings RBa and RBb. The gap size of the oil reservoir 30 is set to be three times or more or 40 μm or more of the gap size in the bearing space in the radial dynamic pressure bearing portions RBa and RBb. This is because a certain amount or more of the lubricating fluid is secured in the lubricating fluid reservoir 33 so as to extend the life of the bearing space so that the lubricating fluid has a sufficient amount of space in the bearing space. Further, each of the radial dynamic pressure bearing portions RB
Capillary seal portions 31a and 31b are provided at both end portions in the axial direction of the bearing space forming the a and RBb so as to sandwich the radial dynamic pressure bearing portions RBa and RBb from both sides in the axial direction. Each of these capillary seal portions 31a, 31b
Is formed by an inclined surface formed on the bearing sleeve 23 side.
The gap between the bearing sleeve 23 and the fixed shaft 12 is gradually enlarged toward the outside of the bearing, and the capillary seal portion 31b disposed on the inner side of the bearing is provided with the oil reservoir 30 described above. Is in communication with The size of the narrow gap continuously expanding in these capillary seal portions 31a, 31b is made from 20 μm to 300 μm.
The liquid surface position of the lubricating fluid is set to be a predetermined position inside each of the capillary seal portions 31a and 31b regardless of whether the motor rotates or stops. Further, a disc-shaped thrust ring 16 is fixed to a tip portion (upper end portion in the drawing) of the fixed shaft 12. The thrust ring 16 is disposed so as to be accommodated in a cylindrical recess formed in the above-described center portion of the bearing base 22 on the upper side in the drawing, and is provided on the bottom wall portion 22 a of the recess of the bearing base 22. The lower thrust dynamic pressure bearing portion SBa is configured by a dynamic pressure surface provided on the lower surface side of the thrust ring 16 in the illustrated direction being arranged close to the dynamic pressure surface in the axial direction. A counter plate 25 is attached to the bearing base 22 so as to be close to the upper surface of the thrust ring 16 in the drawing, and a dynamic pressure surface provided on the lower surface of the counter plate 25 in the drawing. An upper thrust dynamic pressure bearing portion SBb is constituted by a dynamic pressure surface provided on the upper surface side of the thrust ring 16 in the drawing. That is, in each of the pair of thrust dynamic pressure bearing portions SBa, SBb arranged adjacent to each other, the dynamic pressure surface on the bearing base 22 side and the thrust ring 1
The dynamic pressure surface on the sixth side is axially opposed via a narrow gap of several μm, and a set of narrow surfaces arranged at a predetermined distance in the axial direction via the outer peripheral passage of the thrust ring 16. A predetermined lubricating fluid such as an oil or a magnetic fluid is continuously filled in each bearing space formed by the gap. In the present embodiment, both dynamic pressure surfaces provided on both end surfaces of the thrust ring 16 are provided.
The herringbone-shaped thrust dynamic pressure generating grooves (not shown) are recessed so as to be annularly arranged in parallel, and when the hub 21 rotates, the lubricating fluid is generated by the pumping action of both the thrust dynamic pressure generating grooves. The hub 21 is configured so that the hub 21 is axially supported in the thrust direction by the dynamic pressure generated by the lubricating fluid. At this time, the bearing base 2 in this embodiment is
2 is a member having a high hardness, for example, a magnetic steel material such as a nickel alloy having a lower coefficient of thermal expansion than a copper alloy, and the steel material as the nickel alloy is Fe-Ni
(Invar), Fe-Ni-Co (Super Invar) or the like is employed. The surface roughness of the dynamic pressure surface of the bearing base 22 as the high hardness member is formed so as to have an average value of 0.5 μm or less with respect to the surface roughness Rp (center line peak height). The thrust ring 16 made of a low-hardness member is prevented from being worn as much as possible, and is configured to be as close as possible to the state in which the “fit-in” action is completed. On the other hand, the thrust ring 16
Are materials having a hardness lower than that of the bearing base 22, such as Cu (copper), Cu-Al alloy (such as aluminum bronze), Cu-Sn alloy (bronze), and Cu-Sn-P alloy (such as phosphor bronze). ), Cu-Si-Sn-based alloy (silicon bronze-based), Cu-Ni-Zn (such as nickel silver), Cu-Ni-Fe
Copper or copper alloy such as copper alloys (eg, white copper), Cu—Be alloys (eg, beryllium copper), and Cu—Zn alloys (eg, bronze) are used, and a bearing base made of this low hardness member is used. The thrust dynamic pressure generating groove described above is easily formed on 22. The bearing base 2 made of the low hardness member
The surface roughness of the dynamic pressure surface in No. 2 is more than twice (1 μm) the surface roughness Rp (center line peak height) of the surface roughness (0.5 μm) of the fixed shaft 12 made of a hard material described above. It is set to be large, and is configured such that the groove depth of the groove for generating dynamic pressure is maintained at a predetermined amount or more even when the wear by the bearing base 22 made of a high-hardness material is slightly advanced. Further, at both ends in the radial direction of the bearing space constituting the above-mentioned set of thrust dynamic pressure bearing portions SBa, SBb, capillary seal portions 32a, 32b are provided with respective thrust dynamic pressure bearing portions SBa, SBb. Are provided so as to be sandwiched from both sides in the radial direction. Each of these capillary seal portions 32a, 32b
The radially inwardly and outwardly extending gap between the thrust ring 16 and the bearing base 22 is gradually increased by an inclined surface formed on the thrust ring 16 side. The capillary seal portion 32b arranged on the side communicates with the atmosphere on the radial dynamic pressure bearing portion RBa side and the outside of the motor. In addition,
The dimension of the narrow gap continuously expanding in the capillary seal portions 32a and 32b is 20 μm to 300 μm.
When the liquid level position of the lubricating fluid is either rotation or stop of the motor, each of the capillary seal portions 32a, 32
It is set to be a predetermined position inside b. The outer peripheral surface of the above-described thrust ring 16 is formed by recessing the outer peripheral surface of the thrust ring 16 inward in the radial direction. In addition, a lubricating fluid reservoir 34 is formed to ensure a predetermined oil amount. The above-described counter plate 25
Is joined to the bearing base after the above-described respective dynamic pressure bearings are assembled. The joint facing the filling portion of the lubricating fluid is only the joint by the counter plate 25, The other parts with respect to the filling part are integrally formed to secure the airtightness. Further, the joint between the counter plate 25 and the bearing base 22 is joined by an adhesive so as to form a completely sealed structure before the injection of the lubricating fluid, whereby a good sealing property with respect to the lubricating fluid is ensured. Have been.
The adhesive filled in the joint is continuously and continuously filled over the entire periphery of the joint by the capillary force of an annular guide groove (not shown) formed in the joint. This completes the closed structure. The counter plate 25 includes
A thin plate-like stopper plate 27 is provided from the outside (upper side in the figure) via an absorbent cloth 26, and the absorbent cloth 26 and the stopper plate 27 prevent the lubricating fluid from scattering outside even in the worst case. Has become. Further, the thin stopper plate 2 is also provided to the outer portion of the radial dynamic pressure bearing portion RBb on the lower end side in the drawing via the same absorbent cloth 26.
The absorbent cloth 26 and the stopper plate 27 prevent the lubricating fluid from scattering outside even in the worst case. According to this embodiment, the bearing sleeve 23 and the thrust ring 16 made of a low-hardness member are used.
The groove for dynamic pressure generation is easily formed on the bearing shaft 23 and the bearing sleeve 23 and the thrust ring 16 made of a low-hardness member are formed by the “fitting” action between the fixed shaft 12 made of a high-hardness member and the bearing base 22. Even if worn, the surface roughness of the bearing sleeve 23 and the thrust ring 16 is originally set to be large, so that the groove depth of the dynamic pressure generating groove is maintained at a predetermined amount or more for a long period of time. The pressurizing action of the generating groove is also exerted well, and the influence of "fit-in" is eliminated as much as possible. Further, in the present embodiment, the average surface roughness Rp (center line peak height) of the dynamic pressure surface of the fixed shaft 12 and the bearing base 22 made of a high hardness member is brought as close as possible to the state where the “adjustment” is completed. Is formed in a state where
Since the surface roughness of the dynamic pressure surface of the bearing sleeve 23 and the thrust ring 16 made of a low hardness member is set to be at least twice as large as that of the fixed shaft 12 and the bearing base 22, the high hardness member (the fixed shaft 12 and the bearing The wear of the low-hardness members (the bearing sleeve 23 and the thrust ring 16) by the base 22) does not progress rapidly, and the required life of the dynamic pressure bearing device can be obtained. In other words, the average surface roughness Rp of the dynamic pressure surface of each member is set so that the life required for the dynamic pressure bearing device is obtained.
(Center line mountain height) is selected. In particular, in the present embodiment, each rotating member 23,
The degree of contact between the fixing member 12 and the fixing members 12 and 16, that is, the degree of “fit-in” is detected by the acoustic piezoelectric element 3. The detection signal obtained by the acoustic piezoelectric element 3 is recorded on the digital oscilloscope 4. An example of the recorded detection signal will also be described with reference to FIG. That is, when the driving power of the motor is turned off from the steady rotation state, the rotation speed r of the rotating member gradually decreases, and accordingly, the dynamic pressure for floating the rotating member also gradually decreases. Then, at time T1 when the rotation speed r of the rotating member becomes r1, the rotating member starts to contact the fixed member side. From the start of the contact, the rotating member and the fixed member rotate in a contact state, and the acoustic energy generated by the contact between the two members is detected by the acoustic piezoelectric element 3. The acoustic piezoelectric element 3 emits an AE signal as a detection signal having an amplitude corresponding to the intensity of acoustic energy. Therefore, by measuring the amplitude of the detection signal (AE signal) from the acoustic piezoelectric element 3, the strength of contact between the rotating member and the fixed member is detected. The detection signal (AE signal) from the acoustic piezoelectric element 3 continues until a time point T3 at which the spontaneous stop occurs, but reaches a maximum peak state at a time point T2 in the middle. Then, the maximum amplitude AEmax of the AE signal at the time of the maximum peak and the rotation speed r2 corresponding to the maximum amplitude AEmax, and the rotation speed r at the contact start time described above.
Based on the above, it is determined how much “fit-in” has progressed between the rotating member and the fixed member, and then the life of the device is estimated. Although the embodiments of the present invention made by the inventor have been specifically described above, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say. For example, in the above-described embodiment, the acoustic piezoelectric element is arranged on the bottom surface of the frame. However, the arrangement position of the acoustic piezoelectric element is not limited to this. It is possible to arrange them in various positions. The grooves for generating dynamic pressure to which the present invention is applied are:
The present invention is not limited to the herringbone shape as in the embodiment described above, and the present invention can be similarly applied to dynamic pressure generating grooves having various other shapes. Further, in the above-described embodiment, the present invention is applied to a so-called fixed shaft type motor, but the present invention can be similarly applied to a shaft rotating type motor. Furthermore, the present invention can be similarly applied to a dynamic pressure bearing device used other than the above-described HDD motor. In addition to oil, air and various other fluids can be used as a lubricating fluid. The present invention can be similarly applied to those used. As described above, according to the first or third aspect of the present invention, the state of contact between the rotating member and the fixed member in the process of stopping rotation that varies according to the degree of “fit-in” The device life is predicted by detecting the degree of “fit-in” on the basis of the detection result, so that the life of the device can be predicted from the time of shipment of the device. As a result, the reliability of the dynamic bearing device can be improved. Further, in the invention according to claim 2 or 4, since the degree of "fit-in" is detected satisfactorily by the acoustic piezoelectric element, the above-mentioned effect can be obtained reliably. Further, according to the present invention, the degree of "fit-in" can be easily and accurately detected based on the maximum value of the contact strength between the rotating member and the fixed member measured by the acoustic piezoelectric element. Therefore, the above-described effects can be reliably obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an HDD spindle motor including a dynamic bearing device according to an embodiment of the present invention. FIG. 2 is a diagram showing a change in a detection signal obtained by an acoustic piezoelectric element in a rotation stop process. [Description of Signs] 3 Acoustic piezoelectric element 11 Frame 12 Fixed shaft (fixed member) 16 Thrust ring (fixed member) 22 Bearing base (rotating member) 23 Bearing sleeve (rotating member) RBa, RBb Radial dynamic pressure bearings SBa, SBb Thrust dynamic pressure bearing

Claims (1)

Claims 1. A predetermined lubricating fluid is provided in a bearing space defined in a dynamic pressure bearing portion that rotatably supports a rotating member with respect to a fixed member. A dynamic pressure generating groove for generating a dynamic pressure in the lubricating fluid filled in the bearing space is provided on at least one of the opposed dynamic pressure surfaces of the fixed member and the rotating member constituting the dynamic pressure bearing portion, In a life testing device for a hydrodynamic bearing device that supports the rotating member in a floating state with respect to a fixed member based on a dynamic pressure action by a generation groove, the dynamic pressure decreases in a process where the rotation of the rotating member stops naturally. Detecting means for detecting the degree of contact between the rotating member and the fixed member between the time when the rotating member comes into contact with the fixed member and the time when the rotating member stops, and measures the degree of “fitness” between the two members. Dynamic pressure bearing characterized by the following: Location of life inspection apparatus. 2. The detecting means according to claim 1, wherein said detecting means comprises an acoustic piezoelectric element for detecting acoustic energy generated by a contact between the rotating member and the fixed member and measuring a contact strength between the two members. Inspection equipment for dynamic bearings. 3. A predetermined lubricating fluid is provided in a bearing space defined by a dynamic pressure bearing portion rotatably supporting a rotating member with respect to a fixed member, and the dynamic pressure bearing portion is constituted. A dynamic pressure generating groove for generating a dynamic pressure in the lubricating fluid filled in the bearing space is provided on at least one of the opposed dynamic pressure surfaces of the fixed member and the rotating member, and the dynamic pressure generated by the dynamic pressure generating groove is provided. In the method for inspecting the life of a dynamic pressure bearing device for supporting the rotating member in a floating state with respect to a fixed member based on an action, in a process of stopping the rotation of the rotating member, the rotating member becomes a fixed member due to a decrease in dynamic pressure. Detects the degree of contact between the rotating member and the fixed member during the period from contact to stop, measures the degree of “fit-in” between the two members, and predicts the life of the device based on the result. Dynamic pressure characterized by Life test method receiving device. 4. The method according to claim 3, wherein the degree of contact between the rotating member and the fixed member is detected using an acoustic piezoelectric element that detects acoustic energy generated by the contact between the rotating member and the fixed member. A method for inspecting the life of a hydrodynamic bearing device, wherein the strength of contact between a rotating member and a fixed member is measured by the acoustic piezoelectric element. 5. The maximum value of the contact strength between the rotating member and the fixed member measured by the acoustic piezoelectric element according to claim 4, the number of rotations at which the maximum contact strength is generated, and the number of rotations at which the contact starts. Wherein the degree of “fit-in” is determined.