JP4152707B2 - Hydrodynamic bearing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic bearing device in which a rotating member is supported in a non-contact manner by an oil film of lubricating oil generated in a radial bearing gap. This bearing device is a spindle of information equipment such as magnetic disk devices such as HDD and FDD, optical disk devices such as CD-ROM, CD-R / RW and DVD-ROM / RAM, and magneto-optical disk devices such as MD and MO. It is suitable for a motor, a polygon scanner motor of a laser beam printer (LBP), or an electric device such as a small motor such as an axial fan.
[0002]
[Prior art]
In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied or actually used. .
[0003]
This type of hydrodynamic bearing includes a so-called hydrodynamic bearing provided with dynamic pressure generating means for generating dynamic pressure in the lubricating oil in the bearing gap, and a so-called perfect bearing having no dynamic pressure generating means (the bearing surface is a perfect circle). The bearings are roughly classified into shapes.
[0004]
For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk device such as an HDD, a radial bearing portion that supports a shaft member in a non-contact manner in the radial direction and a thrust bearing portion that supports the shaft member in a thrust direction are provided. A dynamic pressure bearing in which a groove for generating dynamic pressure (dynamic pressure groove) is provided on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member is used as the bearing portion (see, for example, Patent Document 1). In order to obtain a high bearing function, this radial bearing portion is often provided at a plurality of locations apart in the axial direction. As the thrust bearing portion, for example, a bearing (so-called pivot bearing) having a structure in which the end surface of the shaft member is supported in the thrust direction by a thrust bearing portion provided on one end side of the housing is used. Normally, the bearing sleeve is fixed at a predetermined position on the inner periphery of the housing, and a seal member is provided on the other end of the housing to prevent the lubricating oil injected into the inner space of the housing from leaking to the outside. There are many.
[0005]
[Patent Document 1]
JP-A-2001-124057 [0006]
[Problems to be solved by the invention]
In this type of hydrodynamic bearing device, the pressure of the lubricating oil increases around the thrust bearing on the one end side of the housing when the bearing rotates due to the shape and dimensional error of the bearing clearance and dynamic pressure groove of the radial bearing. There may be a pressure difference with the lubricating oil around the end seal. For example, taking a dynamic pressure bearing having a herringbone-shaped dynamic pressure groove on the radial bearing surface as an example, if the dynamic pressure groove is accurately formed symmetrically in the axial direction with respect to the axial center, the dynamic pressure The pumping force of the lubricating oil by the groove is balanced on the seal side and the thrust bearing side with respect to the axial center, but the shape of the dynamic pressure groove becomes asymmetric in the axial direction due to manufacturing errors, etc. When the axial dimension on the seal portion side becomes larger than the axial dimension on the thrust bearing portion side, the pumping force of the lubricating oil by the dynamic pressure groove becomes relatively large on the seal portion side with respect to the thrust bearing portion side. Then, due to the differential pressure of this pumping force, the pressure of the lubricating oil from the seal part side toward the thrust bearing part side is applied, which increases the pressure of the lubricating oil around the thrust bearing part, and the pressure with the lubricating oil around the seal part Causes a difference.
[0007]
Then, due to the pressure difference, the shaft member receives an axial force in a direction in which the shaft member is pushed up toward the seal portion (hereinafter, this axial force is referred to as “push-up force”). Normally, a motor incorporating this type of hydrodynamic bearing device has a structure in which the shaft member is pressed against the thrust bearing portion by the magnet's adsorption force, etc., but if the above-mentioned pushing force becomes larger than this pushing force, There is a possibility that the phenomenon of lifting of the member occurs, which may adversely affect the motor and its peripheral parts.
[0008]
An object of the present invention is to prevent the shaft member from being lifted by the above-described pushing force.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a housing, a bearing sleeve provided inside the housing, a shaft member inserted into the inner peripheral surface of the bearing sleeve, an inner peripheral surface of the bearing sleeve, and an outer periphery of the shaft member. A radial bearing portion that supports the shaft member in the radial direction with an oil film of lubricating oil generated in the bearing gap, and a thrust bearing that is provided on one end side of the housing and supports the end surface of the shaft member in the thrust direction And a seal portion provided on the other end side of the housing and forming a seal space between the outer peripheral surface of the shaft member, the bearing sleeve is a porous body made of sintered metal. The inner space of the housing that is formed and sealed with the seal portion is filled with lubricating oil including the inner pores of the bearing sleeve, and the radial bearing portions are provided at a plurality of locations separated in the axial direction. Together with a, is configured as a lubricating oil in the direction of the radial bearing portion provided elsewhere from the radial bearing portion provided to the nearest point on the thrust bearing portion retraction occurs, the bearing sleeve and the shaft member during the relative rotation between the pressure Pt in the lubricating oil near the thrust bearing portion, the pressure Ps of the lubricant near the seal portion, Ri Do a Pt ≦ Ps, the lubricating oil is filled in the internal space of the housing oil surface provides a structure that will be maintained in the sealing space.
[0010]
By configuring the radial bearing portion as described above, the flow of lubricating oil from the radial bearing portion closest to the thrust bearing portion to the other radial bearing side, that is, the lubricating oil flowing from the thrust bearing portion side to the seal portion side flow occurs, the pressure Pt of the lubricating oil around the thrust bearing portion is equal to or pressure Ps of the lubricating oil around the seal portion is lower than this (Pt ≦ Ps). Thereby, generation | occurrence | production of the said raising force with respect to a shaft member can be avoided, and the phenomenon of a shaft member lifting can be prevented.
[0012]
More specifically, the following means can be employed.
[0013]
The first means is that in the radial bearing portion provided at a position closest to the thrust bearing portion, the pumping force of the lubricating oil by the dynamic pressure groove of the radial bearing portion is larger on the thrust bearing portion side than on the seal portion side. Is to configure. With this configuration, the lubricating oil flows from the thrust bearing portion side toward the seal portion side, whereby the pressure of the lubricating oil around the thrust bearing portion becomes higher than the pressure of the lubricating oil around the seal portion. The phenomenon is prevented.
[0014]
As a first means, the dynamic pressure groove of the radial bearing portion provided at the location closest to the thrust bearing portion can be formed asymmetrically in the axial direction. For example, when the dynamic pressure groove has a herringbone shape, the axial dimension on the thrust bearing portion side is larger than the axial dimension on the seal portion side with respect to the axial center of the dynamic pressure groove, or The number of grooves on the bearing side, groove angle, groove depth, etc. are made different from those on the seal portion side. Alternatively, as a first means, the dynamic pressure groove of the radial bearing portion provided at the location closest to the thrust bearing portion is formed symmetrically in the axial direction, while facing the seal portion side end region of the dynamic pressure groove. A clearance part that forms a gap larger than the bearing gap may be provided on the surface of the mating member, and the axial dimension on the seal part side may be made pseudo smaller than the axial dimension on the thrust bearing part side.
[0015]
The second means is that the radial bearing portion provided at the location closest to the thrust bearing portion is compared with the radial bearing portion provided at another location, and the dynamic pressure of the lubricating oil generated in the bearing gap is reduced. It is to make it high. By comprising in this way, the flow of the lubricating oil from the radial bearing portion closest to the thrust bearing portion to the other radial bearing side, that is, the lubricating oil flow from the thrust bearing portion side to the seal portion side occurs, This prevents a phenomenon in which the pressure of the lubricating oil around the thrust bearing portion becomes higher than the pressure of the lubricating oil around the seal portion.
[0016]
The second means includes means for reducing the bearing gap of the radial bearing portion provided at a location closest to the thrust bearing portion to be smaller than the bearing clearance of the radial bearing portion provided at another location, the thrust bearing portion Includes means for making the number of grooves, the groove angle, the groove depth, and the like different between the dynamic pressure groove of the radial bearing portion and the dynamic pressure groove of the other radial bearing portion provided at the closest location. Alternatively, as a second means, the bearing sleeve is formed of a porous material such as sintered metal, and the surface of the bearing surface of the bearing sleeve constituting the radial bearing portion provided at the location closest to the thrust bearing portion is opened. Porosity (surface openness refers to the site where the internal pores of the porous body structure are open to the outer surface, and surface openness refers to the ratio of the total area of surface openness per unit area). The surface area ratio of the bearing surface of the bearing sleeve constituting the radial bearing portion provided at another location may be smaller.
[0017]
Further, as means for satisfying Pt ≦ Ps, in particular, Pt = Ps, the radial bearing portions are provided at a plurality of locations apart in the axial direction, and the radial bearing portion and the thrust bearing portion provided at a location closest to the thrust bearing portion. A space portion having a gap larger than the bearing radius gap of the radial bearing portion can be provided between the two. By providing the space portion, the increase in the pressure of the lubricating oil around the thrust bearing portion is mitigated, and the phenomenon of becoming higher than the pressure of the lubricating oil around the seal portion is prevented. This means can be applied to both a case where the radial bearing portion is configured as a so-called circular bearing (a bearing having no dynamic pressure groove on the bearing surface) and a case where the radial bearing portion is configured as a dynamic pressure bearing.
[0018]
The maximum value of the clearance in the space is preferably 10 times or more the bearing radius clearance. This is due to the following reason. In general, the load capacity W of the fluid dynamic bearing can be expressed by the following equation.
W = W1 · {αωR ⁴ / (ΔR) ² } · β
Here, W: load capacity, W1: dimensionless load capacity determined by bearing specifications, α: lubricating oil viscosity, ω: rotational angular velocity, R: bearing radius, ΔR: bearing radius gap, β: eccentricity.
[0019]
From the above formula, it can be seen that the load capacity W becomes 1/100 when the bearing radius gap ΔR is 10 times larger. Therefore, by making the clearance of the space portion 10 times or more of the bearing radius clearance, the load capacity of the space portion can be reduced to 1/100 (1%) or less of the load capacity of the radial bearing portion. The increase in the pressure of the lubricating oil around the thrust bearing portion can be effectively mitigated.
[0020]
In the above structure, the housing can be formed of a resin material. Resin housings can be formed by injection molding or other molds, so they can be manufactured at lower costs than metal housings made by machining such as turning, and compared to metal housings made by pressing. A relatively high accuracy can be ensured. In particular, by using the bearing sleeve as an insert part and molding the housing with a resin material, it is possible to omit the fixing work by bonding the bearing sleeve to the housing, etc., which is advantageous in simplifying the assembly process. In this case, when the bearing sleeve is formed of sintered metal, the molten resin penetrates into the internal pores from the surface opening of the fixed surface of the bearing sleeve and solidifies during molding, and the solidified portion in the internal pores is solidified. Since the housing and the bearing sleeve are firmly brought into close contact by a kind of anchor effect, a relative fixed position between them does not occur, and a stable fixed state can be obtained.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0022]
FIG. 1 shows a configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device 1 according to this embodiment. This spindle motor is used in a disk drive device such as an HDD, and the hydrodynamic bearing device 1 that rotatably supports the shaft member 2, the disk hub 3 attached to the shaft member 2, and a radial gap. And a motor stator 4 and a motor rotor 5 which are opposed to each other. The stator 4 is attached to the outer periphery of the casing 6, and the rotor 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the casing 6. The disk hub 3 holds one or more disks D such as magnetic disks. When the stator 4 is energized, the rotor 5 is rotated by the exciting force between the stator 4 and the rotor 5, whereby the disk hub 3 and the shaft member 2 are rotated together.
[0023]
FIG. 2 shows a fluid dynamic bearing device (fluid dynamic pressure bearing device) 1 according to the first embodiment. The hydrodynamic bearing device 1 includes a housing 7, a bearing sleeve 8, and a shaft member 2 as components.
[0024]
Between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a of the shaft member 2, the first radial bearing portion R1 and the second radial bearing portion R2 are provided apart from each other in the axial direction. A thrust bearing portion T is provided between the lower end surface 2 b of the shaft member 2 and the inner bottom surface 7 c 2 of the bottom portion 7 c of the housing 7. For convenience of explanation, the description will be given with the thrust bearing portion T side as the lower side and the side opposite to the thrust bearing portion T (the seal portion 7a side) as the upper side.
[0025]
The bearing sleeve 8 is formed in a cylindrical shape, for example, with a porous body made of sintered metal, particularly a sintered body of sintered metal mainly composed of copper. On the inner peripheral surface 8a of the bearing sleeve 8 formed of this sintered metal, two upper and lower regions serving as radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2 are provided apart in the axial direction. For example, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 as shown in FIG. 3 are formed in the two regions. The upper (closer to the seal portion 7a) dynamic pressure groove 8a1 is formed in an axially symmetrical shape with respect to the axial center m1 (the axial dimension from the axial center m1 is X0), but the lower ( The dynamic pressure groove 8a2 on the side close to the thrust bearing portion T is formed in an axially asymmetric shape with respect to the axial center m2. In this example, the axial dimension X1 in the lower region (side closer to the thrust bearing portion T) from the axial center m2 is made larger than the axial dimension X2 in the upper region (side closer to the seal portion 7a) ( X1> X2).
[0026]
The shaft member 2 is formed of, for example, a metal material such as stainless steel, and a lower end portion of the convex spherical shape that forms the thrust bearing portion T in cooperation with the inner bottom surface 7c2 of the bottom portion 7c of the housing 7 at the lower end portion thereof. An end face 2b is provided.
[0027]
The housing 7 is formed by injection molding (insert molding) of resin using a bearing sleeve 8 made of sintered metal as an insert part, and integrally extends from the upper end of the cylindrical side portion 7b to the inner diameter side from the upper end of the side portion 7b. And an annular seal portion 7a and a bottom portion 7c that is continuous with the lower end of the side portion 7b. The inner peripheral surface 7a1 of the seal portion 7a faces the outer peripheral surface 2a of the shaft member 2 via a predetermined seal space S. By the above insert molding, the inner peripheral surface 7b1 of the side portion 7b is the outer peripheral surface 8d of the bearing sleeve 8, the inner side surface 7a2 of the seal portion 7a is the upper end surface 8b of the bearing sleeve 8, and the inner bottom surface 7c1 is below the bearing sleeve 8. The side end surfaces 8c are coupled in close contact with each other. Since the bearing sleeve 8 is formed of a porous sintered metal, the housing 7 and the bearing sleeve 8 are firmly adhered to each other by the anchor effect described above, and a stable fixed state of both is obtained.
[0028]
The hydrodynamic bearing device 1 of this embodiment can be assembled by attaching the shaft member 2 to the housing 7 and the bearing sleeve 8 fixed to each other by the above-described insert molding. That is, the shaft member 2 is inserted into the inner peripheral surface 8 a of the bearing sleeve 8, and the lower end surface 2 b is brought into contact with the inner bottom surface 7 c 2 of the housing 7. Then, the lubricating oil is filled in the internal space of the housing 7 including the internal pores of the bearing sleeve 8 and sealed by the seal portion 7a. The oil level of the lubricating oil is maintained in the seal space S.
[0029]
When the shaft member 2 rotates, the regions (two upper and lower regions) of the inner peripheral surface 8a of the bearing sleeve 8 are opposed to the outer peripheral surface 2a of the shaft member 2 via a radial bearing gap. As the shaft member 2 rotates, dynamic pressure of lubricating oil is generated in the bearing gap, and the shaft member 2 is supported in a non-contact manner in a radial direction by a lubricating oil film formed in the bearing gap. The Thus, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are configured. At the same time, the lower end surface 2 b of the shaft member 2 is contact-supported by the inner bottom surface 7 c 2 of the housing 7. Thereby, the thrust bearing part T which supports the shaft member 2 rotatably in the thrust direction is configured.
[0030]
As described above, of the first radial bearing portion R1 and the second radial bearing portion R2 provided at the two upper and lower locations, the dynamic pressure groove of the second radial bearing portion R2 on the lower side (side closer to the thrust bearing portion T). 8a2 is formed in an axially asymmetric shape with respect to the axial center m2, and the axial dimension X1 of the lower region (side closer to the thrust bearing portion T) from the axial center m2 is the upper region (seal portion 7a). It is larger than the axial dimension X2 on the side close to. Therefore, when the shaft member 2 rotates, the pumping force of the lubricating oil by the dynamic pressure groove 8a2 is relatively large in the lower region (side closer to the thrust bearing portion T) than in the upper region (side closer to the seal portion 7a). Become. Then, due to the differential pressure of the pumping force, the flow of the lubricating oil from the second radial bearing portion R2 side to the first radial bearing portion R1, that is, the lubricating oil from the thrust bearing portion T side to the seal portion 7a side. As a result, the phenomenon that the pressure of the lubricating oil around the thrust bearing portion T becomes higher than the pressure of the lubricating oil around the seal portion 7a is prevented.
[0031]
FIG. 4 shows a fluid dynamic bearing device (fluid dynamic pressure bearing device) 11 according to the second embodiment. In the hydrodynamic bearing device 11, the dynamic pressure groove 8a1 ′ of the first radial bearing portion R1 and the dynamic pressure groove 8a2 ′ of the second radial bearing portion R2 are both formed axially symmetrical, while the second radial bearing portion R2 is The end region on the seal portion 7a side of the dynamic pressure groove 8a2 ′ is opposed to the escape portion 2c provided on the outer peripheral surface 2a of the shaft member 2. The escape portion 2c of the shaft member 2 is provided in a region between the first radial bearing portion R1 and the second radial bearing portion R2, and the clearance between the escape portion 2c and the inner peripheral surface 8a of the bearing sleeve 8 is It is larger than the bearing clearance of the second radial bearing portion R2 (and the first radial bearing portion R1). Therefore, by making the end region of the dynamic pressure groove 8a2 'on the seal portion 7a side to face the relief portion 2c, the axial dimension of the dynamic pressure groove 8a2' on the seal portion 7a side is simulated in the thrust bearing portion T side. It becomes smaller than the axial dimension. Therefore, when the shaft member 2 rotates, the pumping force of the lubricating oil by the dynamic pressure groove 8a2 ′ is relatively lower in the lower region (side closer to the thrust bearing portion T) than in the upper region (side closer to the seal portion 7a). growing. Then, due to the differential pressure of the pumping force, the flow of the lubricating oil from the second radial bearing portion R2 side to the first radial bearing portion R1, that is, the lubricating oil from the thrust bearing portion T side to the seal portion 7a side. As a result, the phenomenon that the pressure of the lubricating oil around the thrust bearing portion T becomes higher than the pressure of the lubricating oil around the seal portion 7a is prevented.
[0032]
FIG. 5 shows the periphery of the thrust bearing portion T in the fluid dynamic bearing device (fluid dynamic pressure bearing device) according to the third embodiment. In this hydrodynamic bearing device, a space portion S1 having a gap C1 larger than the bearing radius gap C0 of the second radial bearing portion R2 is provided between the second radial bearing portion R2 and the thrust bearing portion T.
[0033]
In this embodiment, the lower end surface 2b of the shaft member 2 is formed in a convex spherical shape, and is smoothly continuous with the outer peripheral surface 2a via a connecting portion 2d having a curvature radius smaller than the curvature radius of the lower end surface 2b. . Further, the maximum value of the gap C1 in the space S1 is set to be 10 times or more the bearing radius gap C0 of the second radial bearing portion R2. The dynamic pressure groove of the first radial bearing portion R1 and the dynamic pressure groove of the second radial bearing portion R2 are both formed symmetrically in the axial direction. Other configurations are the same as those of the embodiment shown in FIG.
[0034]
By providing a space portion S1 having a gap C1 larger than the bearing radial gap C0 of the second radial bearing portion R2 between the second radial bearing portion R2 and the thrust bearing portion T, in particular, the gap C1 of the space portion S1. Is set to be 10 times or more of the bearing radius gap C0 of the second radial bearing portion R2, the increase in the pressure of the lubricating oil around the thrust bearing portion T is alleviated, and lubrication around the seal portion 7a is performed. The phenomenon of higher than oil pressure is prevented.
[0035]
【The invention's effect】
According to the present invention, at the time of relative rotation between the bearing sleeve and the shaft member, the pressure Pt of the lubricating oil around the thrust bearing portion is Pt ≦ Ps with respect to the pressure Ps of the lubricating oil around the seal portion. It is possible to prevent the shaft member from being lifted.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a spindle motor for information equipment using a hydrodynamic bearing device according to the present invention.
FIG. 2 is a cross-sectional view showing the hydrodynamic bearing device according to the first embodiment.
FIG. 3 is a cross-sectional view of a bearing sleeve.
FIG. 4 is a cross-sectional view showing a hydrodynamic bearing device according to a second embodiment.
FIG. 5 is an enlarged cross-sectional view showing the periphery of a thrust bearing portion in a hydrodynamic bearing device according to a third embodiment.
[Explanation of symbols]
1 Hydrodynamic bearing device (dynamic pressure bearing device)
11 Fluid bearing device (dynamic pressure bearing device)
2 Shaft member 2a Outer peripheral surface 2b End surface 2c Escape part 7 Housing 7a Seal part 8 Bearing sleeve 8a Inner peripheral surface 8a1, 8a1 'Dynamic pressure groove 8a2 8a2' Dynamic pressure groove R1 First radial bearing part R2 Second radial bearing part T Thrust Bearing part S Seal space S1 Space part

Claims (7)

A housing, a bearing sleeve provided in the housing, a shaft member inserted into the inner peripheral surface of the bearing sleeve, and an inner peripheral surface of the bearing sleeve and an outer peripheral surface of the shaft member; A radial bearing portion that supports the shaft member in a radial direction with an oil film of lubricating oil generated in the bearing gap, a thrust bearing portion that is provided on one end side of the housing and supports an end surface of the shaft member in the thrust direction, and In a hydrodynamic bearing device provided with a seal portion provided on the other end side of the housing and forming a seal space with the outer peripheral surface of the shaft member,
The bearing sleeve is formed of a porous body made of sintered metal,
The internal space of the housing sealed by the seal portion is filled with lubricating oil, including the internal pores of the bearing sleeve,
The radial bearing portion is provided at a plurality of locations separated in the axial direction, has a dynamic pressure groove, and a radial bearing provided at another location from the radial bearing portion provided at a location closest to the thrust bearing portion. It is configured so that the lubricating oil is drawn in the direction of the bearing part,
When the relative rotation between the shaft member and the bearing sleeve, the pressure Pt of the lubricating oil near the thrust bearing portion, the pressure Ps of the lubricating oil near the seal portion, Ri Do a Pt ≦ Ps,
The hydrodynamic bearing device, wherein an oil level of lubricating oil filled in an internal space of the housing is maintained in the seal space .   The radial bearing portion is provided at a plurality of locations apart in the axial direction, and the radial bearing portion has a dynamic pressure groove, and is different from the radial bearing portion provided at a location closest to the thrust bearing portion. The hydrodynamic bearing device according to claim 1, wherein the lubricating oil is drawn in a direction of a radial bearing portion provided at a location.   The radial bearing portion provided at a location closest to the thrust bearing portion is configured such that the pumping force of the lubricating oil by the dynamic pressure groove is larger on the thrust bearing portion side than on the seal portion side. The hydrodynamic bearing device according to claim 2.   The radial bearing portion is provided at a plurality of locations separated in the axial direction, and the radial bearing portion is disposed between the radial bearing portion provided at a location closest to the thrust bearing portion and the thrust bearing portion. The hydrodynamic bearing device according to claim 1, wherein a space having a gap larger than the bearing radius gap is provided.   The hydrodynamic bearing device according to claim 4, wherein a maximum value of the gap in the space is 10 times or more of the bearing radius gap.   6. The hydrodynamic bearing device according to claim 1, wherein the bearing sleeve is made of sintered metal.   The hydrodynamic bearing device according to claim 1, wherein the housing is made of a resin material.

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