JP3633992B2 - Hydrodynamic bearing device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a hydrodynamic bearing device used for a polygon motor used for optical scanning such as a copying machine or a laser beam printer (LBP), a spindle motor for a hard disk, or the like.
[0002]
[Prior art]
Polygon mirrors, that is, polygon mirrors that rotate a polygon mirror with a motor, irradiate the polygonal reflecting surface with a laser beam and scan the reflected light are used in optical scanning units such as copying machines and laser beam printers. The Various types of polygon motors have been conventionally used, but dynamic pressure bearings have been conventionally used in order to meet demands for miniaturization and high speed of polygon motors.
[0003]
In this case, the shaft is inserted inside the cylindrical sleeve fixed to the substrate, the end of the shaft is supported on a thrust receiver that closes the lower end opening of the sleeve, and the rotor is fixed to the upper portion of the shaft. The polygon mirror is fixed to the shaft, and the polygon mirror is rotated at a high speed by rotating the rotor together with the shaft. A herringbone groove for generating dynamic pressure is formed on one or both of the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, and a lubricant is filled between the sleeve and the shaft.
[0004]
For example, FIG. 7 shows a part of the dynamic pressure bearing portion of the polygon motor described above.
The vertical sleeve A fixed to the circuit board of the polygon motor has a cylindrical inner peripheral surface B, and a thrust receiver C is fitted to the lower end opening so as to close it. The shaft D, on which the rotor is fixed at the upper end, is provided with herringbone-like dynamic pressure generating grooves F, G on the upper and lower portions of the outer peripheral surface E. The shaft D is formed in the cylindrical shape of the sleeve A. The groove F is inserted into the peripheral surface B, both grooves F and G face the cylindrical inner peripheral surface B, and the lower end surface H of the shaft D formed on the curved surface faces the spiral groove formed in the central portion of the thrust receiver C. doing. A lubricant such as oil is filled between the cylindrical inner peripheral surface B of the sleeve A and the outer peripheral surface E of the shaft D.
[0005]
At the upper and lower ends of the inner peripheral surface B of the sleeve A, an annular upper taper surface I for the lubricant seal and a lower portion where a gap with the outer peripheral surface E of the shaft D expands outward in the axial direction. A side taper surface J is formed, and the outflow of the lubricant filled between the cylindrical inner peripheral surface B of the sleeve A and the outer peripheral surface E of the shaft D is prevented at both the taper surfaces I and J, and is held therebetween. ing. Both the tapered surfaces I and J are formed substantially symmetrically and form a reservoir of lubricant on the tapered surfaces I and J, and their holding volumes are substantially equal. A lubricant is also filled between the thrust receiver C and the lower end surface H of the shaft D.
[0006]
[Problems to be solved by the invention]
By the way, in the above-described hydrodynamic bearing device, when the lubricant is filled between the cylindrical inner peripheral surface B of the sleeve A and the outer peripheral surface E of the shaft D, the shaft D is inserted into the inner peripheral surface B of the sleeve A from above. In the state in which only the lower end portion of the sleeve A is inserted, the lubricant is applied in an annular shape across the upper end opening surface of the sleeve A and the outer peripheral surface E of the shaft D, and the shaft D is lowered, that is, inserted into the sleeve A from this state. The lubricant is gradually drawn into the gap between the sleeve A and the shaft D, and finally filled between the tapered surfaces I and J.
[0007]
However, when the lubricant filling method described above is employed, the peripheral surface of the lower end portion of the shaft D is wetted with the lubricant, so that even if the lubricant is sealed with the lower tapered surface J, the lubricant remains on the lower end portion of the shaft D. Due to the wettability, it is easy to flow out along this peripheral surface, and the lubricant does not stay on the taper surface J because of the action of gravity, and there is a problem that the upper taper surface I is depleted of the lubricant and is stable. Rotation performance will not be obtained. In addition, since the shaft D rotates at a high speed when the motor rotates, the lubricant on the peripheral surface of the shaft D is likely to be scattered, resulting in further progress of the above-described lubricant depletion.
[0008]
The present invention has been made in consideration of such problems of the prior art. The object of the present invention is to prevent the lubricant from being depleted and to improve the function of retaining the lubricant. An object of the present invention is to provide a hydrodynamic bearing device capable of ensuring stable rotation performance.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the hydrodynamic bearing device according to the present invention, a vertical sleeve having a cylindrical inner peripheral surface, and a cylinder that is inserted through the inner peripheral surface of the sleeve and faces the inner peripheral surface. A vertical shaft having a cylindrical outer peripheral surface and a thrust receiver attached to the lower end opening of the sleeve and supporting the lower end of the shaft, and dynamic pressure is applied to one or both of the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft In the hydrodynamic bearing device in which the groove for generation is formed, the lubricant is filled between the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, and the shaft is rotatably supported with respect to the sleeve.
The upper and lower end portions of the inner peripheral surface of the sleeve are formed with an annular upper tapered surface and a lower tapered surface for a lubricant seal in which a gap between the outer peripheral surface of the shaft expands outward in the axial direction. An annular second tapered surface for a lubricant seal is formed on the outer peripheral portion of the lower tapered surface of the lower end portion of the sleeve so that a gap between the thrust receiver and the thrust receiver expands radially outward. The surface and the second tapered surface are communicated with each other via an annular narrow portion between the sleeve and the thrust receiver.
[0010]
In this case, the volume between the upper tapered surface and the shaft is preferably larger than the volume between the lower tapered surface and the shaft. Further, it is preferable that a groove for generating dynamic pressure is formed on a portion of the upper surface of the thrust receiver facing the shaft, and an oil repellent is applied to the outer peripheral portion of the groove on the upper surface of the thrust receiver. Furthermore, you may apply | coat an oil repellent agent to the surface of the said narrow part, and the surface of a 2nd taper surface.
[0011]
[Action]
In the hydrodynamic bearing device configured as described above, the outer peripheral portion of the lower tapered surface of the lower end portion of the sleeve is connected to the thrust receiver via the annular narrow portion between the sleeve and the thrust receiver. Since the annular second taper surface for the lubricant seal in which the gap of the seal expands outward in the radial direction is formed in communication, the lubrication that has been held by the lower taper surface due to the weight of the lubricant itself or for some other reason Even if the agent is about to flow out of the seal portion, the narrow portion first becomes resistance to the outflow of the lubricant, so that the lubricant cannot easily flow out from the lower taper surface. Even if it flows out and flows out, the lubricant is taper-sealed by the second tapered surface located on the outer peripheral side, and the outflow of the lubricant to the outside is greatly suppressed.
[0012]
Here, if the volume between the upper tapered surface and the shaft is larger than the volume between the lower tapered surface and the shaft, the amount of lubricant is increased so as to retain extra lubricant on the upper tapered surface in advance. Even if the lubricant flows out from the lower tapered surface to the second tapered surface through the narrowed portion, the lubricant is not depleted and the bearing performance can be maintained over a long period of time. In addition, if a groove for generating dynamic pressure is formed in a portion of the upper surface of the thrust receiver facing the shaft, and an oil repellent is applied to the outer periphery of the groove on the upper surface of the thrust receiver, the lubricant on the thrust receiver is grooved. It is possible to prevent the oil from easily flowing out of the outer peripheral direction from the portion. Further, if an oil repellent is applied to the surface of the narrowed portion and the surface of the second tapered surface, the lubricant is more effectively discharged from the lower tapered surface. Can be suppressed.
[0013]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. 1 is a cross-sectional view of an essential part of the first embodiment of the present invention, FIG. 2 is a cross-sectional view showing the overall structure, FIG. 3 is a partially enlarged view of FIG. 1, FIG. 4 is a perspective view of a thrust receiver, and FIG. FIG. 6 is a sectional view showing the overall configuration of the second embodiment of the present invention.
[0014]
First, the overall structure of a polygon motor M to which the present invention is applied will be described with reference to FIG. On the circuit board 2 made of an iron plate or the like, a vertical cylindrical sleeve 6 made of a copper alloy or the like and having a cylindrical inner peripheral surface 4 is fixed by caulking or the like. A substantially disc-shaped thrust receiver 8 is fitted into the lower end opening of the sleeve 6, the shaft 10 is inserted through the upper end opening of the sleeve 6, and the thrust receiving surface 12 at the lower end of the shaft 10 is supported on the thrust receiver 8. ing.
[0015]
A rotor hub 14 is fixed to the upper end portion of the shaft 10 by press-fitting or the like, a substantially covered cylindrical rotor yoke 16 is fixed to the lower surface of the rotor hub 14, and an annular magnet 18 is attached to the inner peripheral surface of the cylindrical portion of the rotor yoke 16. At the same time, the stator 20 fixed to the central portion of the outer peripheral surface of the sleeve 6 by caulking or the like faces the rotor magnet 18 through a radial gap. An annular recess 2 by bending is formed on the outermost peripheral portion of the rotor yoke 16, and a dynamic balance is achieved by filling an appropriate amount of a putty or the like in an appropriate position of the annular recess 22.
[0016]
For example, a regular hexagonal polygon mirror 24 is fitted on the outer periphery of the rotor hub 14, and is sandwiched between the rotor hub 14 by a clamp spring 28 attached to the upper end of the shaft 10 with a screw 26.
[0017]
The shaft 10 inserted into the sleeve 6 has a cylindrical outer peripheral surface 30 that opposes the inner peripheral surface 4 of the sleeve 6, and herringbone-like dynamic pressure generating grooves 32, 34 at the upper and lower portions of the outer peripheral surface 30. Is engraved. As shown in FIG. 3, a lubricant 36 such as oil is filled between the inner peripheral surface 4 of the sleeve 6 and the outer peripheral surface 30 of the shaft 10, and due to the relative rotation between the sleeve 6 and the shaft 10. The lubricant pressure in the central portion of the grooves 32 and 34 is increased, and each of them forms a radial dynamic pressure bearing portion.
[0018]
The upper and lower end portions of the inner peripheral surface 4 of the sleeve 6 are provided with an annular upper tapered surface 36 and a lower portion for a lubricant seal in which a gap with the outer peripheral surface 30 of the shaft 10 expands outward in the axial direction. A side taper surface 38 is formed, and the upper taper surface 36 is formed with a larger volume than the lower taper surface 38. The upper tapered surface 36 and the lower tapered surface 38 prevent the lubricant 36 from flowing out from the inner peripheral surface 4 of the sleeve 6, and the lubricant 36 is filled between the inner and outer peripheral surfaces 4 and 30 therebetween. Become. The lower tapered surface 40 is closer to the lower end side of the shaft 10 than in the conventional case, and is adjacent to the thrust bearing portion.
[0019]
An annular second taper surface 42 for a lubricant seal is formed on the outer peripheral portion of the lower taper surface 40 at the lower end of the sleeve 6 so that the gap with the thrust receiver 8 expands radially outward. The lower tapered surface 40 and the second tapered surface 42 communicate with each other through an annular narrow portion 44 between the sleeve 6 and the thrust receiver 8.
[0020]
The thrust receiver 8 is made of a cermet such as alumina having excellent wear resistance, and a portion of the upper surface of the thrust receiver 8 facing the shaft 10 is for generating a spiral dynamic pressure as shown in FIG. A groove 46 is engraved. An oil repellent is applied to the outer peripheral portion of the upper surface of the thrust receiver 8, that is, the portion facing the open end of the lower tapered surface 40. In this case, it is necessary to apply the oil repellent to the outer peripheral portion of the groove 46 accurately and in an appropriate amount, and if it is less, the lubricant filled between the thrust receiver 8 and the shaft 10 tends to flow out. If this is the case, there will be a problem that the oil repellent itself will flow out.
[0021]
Therefore, in this embodiment, the following lubricant application method is employed. That is, first, as shown in FIG. 5A, the lubricant 36a is thinly applied to the thrust bearing portion on the upper surface of the thrust receiver 8, that is, the groove 46 portion, after the processing of the groove 46 is completed. Next, as shown in FIG. 5B, a predetermined amount of an oil repellent 48 is applied to the outer peripheral portion of the groove 46 and baked. At this time, the oil repellent 48 does not flow into the groove 46 due to the lubricant 36a. Thereafter, as shown in FIG. 3C, a prescribed amount of the lubricant 36b is applied to the upper surface of the lubricant 36a, that is, the inside of the oil repellent 48. Thereby, the oil repellent agent 48 can be applied without entering the groove 46 portion, and the application amount can be easily managed.
[0022]
As shown in FIG. 4, three notches 50 for air bleeding are formed at equal intervals on the outer periphery of the thrust receiver 8. As shown in FIGS. 1 and 3, each notch 50 faces the second tapered surface 42 of the sleeve 6, and the expansion and contraction of the lubricant or the like due to air bleeding and temperature change when the lubricant 36 is filled. It also serves as a breathing opening.
[0023]
In the hydrodynamic bearing device having such a configuration, when the lubricant 36 is injected, the thrust bearing portion is filled with an appropriate amount of the lubricant 36 on the thrust receiver 8 as described above, and the radial bearing is also provided. The bearing 36 is filled with the lubricant 36 as described in the prior art. In the present embodiment, since the lower tapered surface 40 of the sleeve 6 is disposed opposite to the lower end portion of the shaft 10, even if the lower end portion of the shaft 10 is wet with the lubricant when the lubricant is charged, FIG. As shown in FIG. 3, the lubricant 36 is sealed with a taper seal structure including this portion, and the lubricant 36 is prevented from flowing out. Further, the lubricant 36 is filled with a necessary amount or more, and excess lubricant is held on the upper tapered surface 38.
[0024]
When the motor M is driven, the shaft 10 rotates at a high speed, and along with this rotation, the lubricant 36 on the lower tapered surface 40 tends to flow partially toward the lower end along the axial circumferential surface due to centrifugal force. The other lubricant 36 tends to flow along the tapered surface 40 in the outer peripheral direction. The lubricant 36 that is about to flow to the lower end side of the shaft is prevented from spreading further by the action of the oil repellent on the thrust receiver 8, and the lubricant 36 that is about to flow toward the outer circumference is the sleeve 6. The narrow part 44 between the thrust receiver 8 and the thrust receiver 8 serves as a resistance against the outflow of the lubricant 36, and the outflow of the lubricant 36 is stopped by the narrow part 44.
[0025]
Even if the lubricant 36 flows out from the narrowed portion 44, the second tapered seal structure by the second tapered surface 42 exists on the outer peripheral side of the narrowed portion 44. As shown by a two-dot chain line in FIG. 3, the taper is sealed, and the outflow to the outside is reliably prevented. Here, the excess lubricant 36 held on the upper tapered surface 38 is in such an amount that the lubricant between the sleeve 6 and the shaft 10 is not depleted even if the lubricant 36 flows out to the second tapered surface 42. Is set.
[0026]
In the above embodiment, if the surface of the sleeve 6 and the second tapered surface 42 constituting the narrowed portion 42 are not only subjected to the oil repellent treatment, but also the outer peripheral portion of the upper surface of the thrust receiver 8, the above-described sealing effect can be ensured. It becomes.
[0027]
Next, FIG. 6 shows a second embodiment in which the present invention is applied to an inner rotor type polygon motor M ′. In the figure, the same reference numerals as those described above indicate the same or corresponding elements.
[0028]
As in the case of the first embodiment, the sleeve 6 fixed to the circuit board 2 is supported by a dynamic pressure bearing in the radial direction and the thrust direction, and is attached to the rotor hub 14 fixed to the upper end portion of the shaft 10. A cylindrical portion 14 ′ is provided in the vicinity of the outer periphery of the sleeve 6. A rotor magnet 18 is mounted on the outer peripheral surface of the cylindrical portion 14 ′ via a cylindrical yoke 16.
[0029]
On the circuit board 2, an annular stator 20 is disposed so as to face the outer peripheral surface of the rotor magnet 18, and this is fixed to the circuit board 2 by a resin-made annular holder 52.
[0030]
As mentioned above, although the Example of the hydrodynamic bearing apparatus of this invention was described, this invention is not limited to this Example, and it cannot be overemphasized that various changes are possible in the range which does not deviate from the main point of this invention. .
[0031]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
Since the annular second tapered surface for the lubricant seal is formed in communication with the outer peripheral portion of the lower tapered surface of the lower end portion of the sleeve via the annular narrow portion between the sleeve and the thrust receiver, the lower tapered surface Even if the retained lubricant tries to flow out of this seal part for some reason, the lubricant can first stop at the narrow part, and even if the lubricant flows out through the narrow part, The lubricant can be taper-sealed with the second taper surface positioned, the outflow of the lubricant to the outside can be reliably suppressed, and stable bearing performance of the dynamic pressure bearing can be ensured.
[0032]
In addition, if the volume between the upper tapered surface and the shaft is larger than the volume between the lower tapered surface and the shaft, the amount of lubricant is increased in advance so that excess lubricant is retained on the upper tapered surface. Even if the lubricant flows out from the lower taper surface to the second taper surface through the narrowed portion, the lubricant does not run out and the bearing performance can be maintained over a long period of time. is there. Furthermore, if a groove for generating dynamic pressure is formed in a portion of the upper surface of the thrust receiver facing the shaft, and an oil repellent is applied to the outer periphery of the groove on the upper surface of the thrust receiver, the lubricant on the thrust receiver is grooved. It is possible to prevent the oil from easily flowing out from the outer peripheral direction, and by applying an oil repellent to the surface of the narrow portion and the surface of the second taper surface, the outflow of the lubricant from the lower taper surface is more effectively suppressed. It can be done.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part showing a first embodiment when the hydrodynamic bearing device of the present invention is applied to a polygon motor.
FIG. 2 is a cross-sectional view showing the overall configuration of the polygon motor of the first embodiment.
3 is an enlarged cross-sectional view of a lower tapered surface portion of FIG. 1. FIG.
4 is a perspective view of the thrust receiver of FIG. 1. FIG.
5 is a front view of each step for explaining the oil-repellent treatment of the thrust receiver in FIG. 1. FIG.
FIG. 6 is an overall sectional view showing a second embodiment when the hydrodynamic bearing device of the present invention is applied to a polygon motor.
FIG. 7 is a partial cross-sectional view showing a conventional hydrodynamic bearing device.
[Explanation of symbols]
4 Cylindrical inner peripheral surface 6 Sleeve 8 Thrust receiver 10 Shaft 30 Cylindrical outer peripheral surfaces 32, 34, 46 Groove 36 Lubricant 38 Upper tapered surface 40 Lower tapered surface 42 Second tapered surface 44 Narrow part

Claims (4)

A vertical sleeve having a cylindrical inner peripheral surface, a vertical shaft having a cylindrical outer peripheral surface that is inserted through the inner peripheral surface of the sleeve and faces the inner peripheral surface, and a lower end opening of the sleeve. A thrust receiver that supports a lower end portion of the shaft, and a dynamic pressure generating groove is formed in one or both of the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, and the inner peripheral surface of the sleeve In the hydrodynamic bearing device in which a lubricant is filled between the outer peripheral surface of the shaft and the shaft is rotatably supported with respect to the sleeve.
An annular upper tapered surface and a lower tapered surface for a lubricant seal in which a gap between the outer peripheral surface of the shaft and the outer peripheral surface of the shaft expands outward in the axial direction at an upper end portion and a lower end portion of the inner peripheral surface of the sleeve. An annular second taper surface for a lubricant seal in which a gap between the thrust receiver and the outer periphery of the lower taper surface at the lower end portion of the sleeve is expanded radially outward. And the lower tapered surface and the second tapered surface communicate with each other through an annular narrow portion between the sleeve and the thrust receiver. 2. The hydrodynamic bearing device according to claim 1, wherein a volume between the upper tapered surface and the shaft is larger than a volume between the lower tapered surface and the shaft. A groove for generating a dynamic pressure is formed in a portion of the upper surface of the thrust receiver facing the shaft, and an oil repellent is applied to an outer peripheral portion of the groove on the upper surface of the thrust receiver. 1. The hydrodynamic bearing device according to 1. The hydrodynamic bearing device according to claim 1, wherein an oil repellent is applied to a surface of the narrow portion and a surface of the second tapered surface.

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