JP5362634B2 - Hydrodynamic bearing device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device using gas as a fluid, such as an air bearing for a polygon mirror motor of a laser beam printer.

  In a hydrodynamic bearing device using a gas such as air as a fluid, ceramics having excellent wear resistance is used as a bearing material. As a method of manufacturing a bearing sleeve made of this ceramic material, a method of forming a bearing sleeve by powder molding is known (Patent Document 1).

  However, in general, in powder molding, the dimensional accuracy after sintering deteriorates, so that it is necessary to finish with a large machining allowance in order to ensure accuracy. Usually, the depth of the dynamic pressure groove is about several μm, so if the grinding allowance after sintering increases, the dynamic pressure groove disappears by grinding.

  On the other hand, in consideration of grinding allowance, when molding in a shape with a deep dynamic pressure groove in advance, the groove depth exceeds the spring back amount of the molded product, and the molded product cannot be removed from the mold. There is a possibility of damaging the dynamic pressure groove by forcibly removing it.

  As a method for producing a bearing sleeve, a ceramic injection molding method using ceramic powder, that is, a CIM (ceramic injection molding) molding method is known (Patent Document 2). In this manufacturing method, a cylindrical resin core having a convex portion on the outer periphery for transferring and forming a dynamic pressure groove is placed inside a mold having a bearing sleeve-shaped cavity, and ceramic powder and a binder are kneaded. The molding material made in this way is injection-molded. The molded body is placed in a sintering furnace and heated to thermally decompose the binder component and thermally decompose the resin core to extinguish it.

  However, in the manufacturing method described above, it is necessary to thermally decompose the resin core for each bearing sleeve, which causes problems in terms of productivity and cost.

JP 2006-38076 A Japanese Patent Laid-Open No. 2008-244103

  As described above, since all of the conventional techniques form dynamic pressure grooves at the stage of forming a bearing sleeve using a ceramic material, in Patent Document 1, if the grinding allowance after sintering is large, , There is a problem that the dynamic pressure groove disappears due to grinding, the molded product cannot be removed from the mold, or the dynamic pressure groove may be damaged by being forcibly removed. It is necessary to thermally decompose the resin core for each sleeve, and there is a problem in terms of productivity and cost.

  An object of the present invention is to achieve low cost and high accuracy as a dynamic pressure bearing device including a bearing sleeve or a shaft member having a dynamic pressure groove and a manufacturing method thereof.

  The inventors of the present application paid attention to the above-mentioned problems of the prior art and made various studies. As a result, it has been found that the shape of the molded product of the bearing sleeve or the shaft member at the CIM molding stage is a major factor for reducing the cost and increasing the accuracy of the hydrodynamic bearing device.

  And, as a bearing sleeve or shaft member, use a CIM molded product with a simple shape and no dynamic pressure groove on the bearing surface, and form a high precision dynamic pressure groove by ultrashort pulse laser processing on this bearing surface. Inspired by two means of creating synergistic benefits.

  The hydrodynamic bearing device according to the present invention is a hydrodynamic bearing device including a bearing sleeve or a shaft member in which a hydrodynamic groove is formed on the bearing surface, wherein the bearing sleeve or the shaft member has a shape without the hydrodynamic groove on the bearing surface. The ceramic injection molded article is used, and the bearing surface is provided with a dynamic pressure groove formed by ultrashort pulse laser processing.

  According to a second aspect of the present invention, in the hydrodynamic bearing device according to the first aspect, the bearing surface of the bearing sleeve or the shaft member is finished by grinding.

  According to a third aspect of the present invention, in the hydrodynamic bearing device according to the first or second aspect, the ceramic material of the bearing sleeve or the shaft member is zirconia.

  According to a fourth aspect of the present invention, in the hydrodynamic bearing device according to any one of the first to third aspects, the hydrodynamic groove is processed by continuous hitting with an ultrashort pulse laser. is there.

  According to a fifth aspect of the present invention, in the hydrodynamic bearing device according to any one of the first to fourth aspects, the pulse width of the ultrashort pulse laser is 1 to 100 ns.

  A sixth aspect of the present invention is the fluid dynamic bearing device according to any one of the first to fifth aspects, wherein the bearing surface of the bearing sleeve is at least one of an inner peripheral surface and an end surface. It is.

  The invention according to claim 7 is the dynamic pressure bearing device according to any one of claims 1 to 5, wherein the bearing surface of the shaft member is at least one of an outer peripheral surface and an end surface. is there.

  According to an eighth aspect of the present invention, in the dynamic pressure bearing device according to the sixth or seventh aspect, the dynamic pressure groove formed on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member has a herringbone shape. It is characterized by.

  A ninth aspect of the present invention is the dynamic pressure bearing device according to the sixth or seventh aspect, wherein the dynamic pressure groove formed on the end surface of the bearing sleeve or the shaft member has a spiral shape. is there.

  The invention according to claim 10 is the fluid dynamic bearing device according to any one of claims 1 to 5, wherein the bearing sleeve has a bottom portion, and the bearing surface of the bearing sleeve is at least an inner peripheral surface and a bottom top surface. It is characterized by being one.

  The invention according to claim 11 is the fluid dynamic bearing device according to claim 10, wherein the dynamic pressure groove formed on the inner peripheral surface of the bearing sleeve has a herringbone shape, and the dynamic pressure groove formed on the upper surface of the bottom portion. Is a spiral shape.

The invention of claim 12 is the hydrodynamic bearing device according to any one of claims 1 to 11,
The hydrodynamic bearing device supports the bearing sleeve or the shaft member by the hydrodynamic action of air.

  A method for manufacturing a hydrodynamic bearing device according to the invention of claim 13 is a method for manufacturing a hydrodynamic bearing device including a bearing sleeve or a shaft member having a hydrodynamic groove formed on a bearing surface, wherein the bearing sleeve or the shaft member includes: It is manufactured from a step of forming a dynamic pressure groove on a bearing surface by ceramic injection molding, degreasing and sintering, and a step of forming a dynamic pressure groove on the bearing surface by an ultrashort pulse laser. To do.

  A fourteenth aspect of the invention is characterized in that, in the method of manufacturing a hydrodynamic bearing device according to the thirteenth aspect, the manufacturing process of the bearing sleeve or the shaft member further includes a step of grinding the bearing surface.

  A fifteenth aspect of the invention is characterized in that, in the method of manufacturing a dynamic pressure bearing device according to the thirteenth aspect, the dynamic pressure groove is processed by continuous hitting with an ultrashort pulse laser.

The invention of claim 16 is the method of manufacturing a hydrodynamic bearing device according to claim 15, wherein the ultrashort pulse laser is a fundamental wave of an ultrashort pulse Q-switched YAG laser having a pulse width of 1 ns to 100 ns, moving together using any one of second harmonic wave and third harmonic wave, the processing by the continuous RBI, the laser power density to a value in the range of ^{1GW / cm 2 ~100GW / cm 2} , the diameter of the beam spot of the laser It is characterized by being made smaller than the width of the pressure groove.

  According to a seventeenth aspect of the present invention, in the method for manufacturing a hydrodynamic bearing device according to the fifteenth or sixteenth aspect, the laser beam spot optical system is electrically controlled and machined during the processing by the continuous hitting point. It is characterized in that it is swung by at least one control of the mechanical control.

  The invention according to claim 18 is the method of manufacturing a hydrodynamic bearing device according to any one of claims 13 and 15 to 17, wherein the ceramic sintered body to be processed is submerged in the laser processing. It arrange | positions or it pours flowing water on a ceramic sintered compact, It is characterized by the above-mentioned.

  The invention according to claim 19 is the method of manufacturing a hydrodynamic bearing device according to any one of claims 13 and 15 to 18, wherein the laser beam irradiation direction is ceramic sintered during the laser processing. It is characterized by being inclined with respect to a line perpendicular to the processed surface of the body.

  According to a twentieth aspect of the present invention, in the method for manufacturing a hydrodynamic bearing device according to the thirteenth aspect, a hard coating having a hardness equal to or higher than the hardness of the ceramic material of the molded product is applied to the ceramic injection mold. It is characterized by this.

  The invention of claim 21 is the method of manufacturing a hydrodynamic bearing device according to claim 20, wherein the hard coating is selected from titanium nitride (TiN), diamond-like carbon (DLC), and chromium nitride (CrN). It is characterized by being a hard film.

  A twenty-second aspect of the invention is a bearing sleeve or a shaft member based on the method for manufacturing a hydrodynamic bearing device according to any one of the thirteenth to twenty-first aspects.

  According to the hydrodynamic bearing device and the manufacturing method thereof of the present invention, since the bearing sleeve or the shaft member is a simple CIM molded product having no dynamic pressure groove on the bearing surface, the accuracy of the CIM molded product after firing is improved. Since it is more excellent, the grinding cost in the subsequent process can be kept low, or grinding can be omitted. Therefore, as a hydrodynamic bearing device including a bearing sleeve or a shaft member having a hydrodynamic groove and a manufacturing method thereof, low cost and high accuracy can be achieved.

  Further, coupled with the fact that the bearing sleeve or the shaft member is a simple CIM molded product having no dynamic pressure groove on the bearing surface, the dynamic pressure groove is formed by ultrashort pulse laser processing, so the processing site In addition, the groove depth can be easily controlled without leaving a heat-affected layer, and variations in groove dimensions can be suppressed and finished with high accuracy, so that the bearing function can be enhanced.

Furthermore, as the ultrashort pulse laser, any one of the fundamental wave, the second harmonic wave, and the third harmonic wave of the ultrashort pulse Q-switched YAG laser having a pulse width of 1 ns to 100 ns is used, and the laser beam spot during processing by the continuous RBI, as the energy density of the laser, by making the range of ^{1GW / cm 2 ~40GW / cm 2} , the processing efficiency is excellent, like burr to residual and the processing surface of the heat-affected layer is suppressed And the quality will be good.

  The laser beam spot optical system is oscillated by at least one of electrical control and mechanical control during machining with continuous hitting points, so that the hydrodynamic groove surface (groove bottom) can be smoothed. The flatness of the groove bottom is improved. Thereby, the shape of the dynamic pressure groove and the quality of the processed removal surface can be improved.

  During laser processing, if the workpiece of the bearing sleeve or shaft member is placed in the water or processed by running the workpiece under running water, the removal processing is further improved, and the second harmonic and the third harmonic laser are It can be processed without being absorbed by water, and the processed surface can be finished beautifully.

1 is a longitudinal sectional view of a fluid dynamic bearing device according to a first embodiment of the present invention. It is a longitudinal cross-sectional view of the bearing sleeve which is a component of the said hydrodynamic bearing apparatus. It is a figure which shows the manufacturing process of the said bearing sleeve. It is a longitudinal cross-sectional view which shows a CIM shaping | molding process. It is a longitudinal cross-sectional view which shows the laser processing of the dynamic pressure groove of a bearing sleeve. It is a schematic diagram which shows the flow of a process of a bearing sleeve. It is a longitudinal cross-sectional view which shows the bearing sleeve which is a component of 2nd Embodiment of this invention. It is a schematic diagram which shows the flow of a process of the bearing sleeve in 2nd Embodiment. It is a longitudinal cross-sectional view of the dynamic pressure bearing apparatus which concerns on 3rd Embodiment of this invention. It is a top view of the shaft member which is a component of the said hydrodynamic bearing apparatus. It is a schematic diagram which shows the flow of a process of a shaft member. It is a longitudinal cross-sectional view which shows the bearing sleeve which is a component of the 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  1 to 6 show a first embodiment of the present invention. As shown in FIG. 1, the hydrodynamic bearing device 1 mainly includes a housing 4, a bearing sleeve 3 incorporated and fixed on the inner periphery, and a shaft member 2 inserted on the inner periphery. A dynamic pressure groove 3a11 is formed in the bearing surface 3a1 of the inner peripheral surface 3a of the bearing sleeve 3. A radial gap 5 is formed between the bearing surface 2 a 1 of the outer peripheral surface 2 a of the shaft member 2 and the bearing surface 3 a 1 of the bearing sleeve 3. In order to support the axial load, the end surface 2 b of the shaft member 2 is disposed to face the thrust bearing portion 4 b formed on the upper surface of the bottom portion 4 a of the housing 4. Although illustration is omitted, a dynamic pressure groove is also formed in the thrust bearing portion 4b. The shaft member 2 is connected to a rotor of a motor (not shown). FIG. 1 shows a state in which the shaft member 2 is rotating. The shaft member 2 is floated by the dynamic pressure action of air generated in the radial gap 5 and the thrust gap 6, and the bottom portion of the shaft sleeve 3 and the housing 4. 4a is supported in a non-contact state. Note that the radial gap 5 and the thrust gap 6 are exaggerated for easy understanding.

  FIG. 2 shows a bearing sleeve 3 which is a component of the embodiment. The bearing sleeve 3 is formed in a cylindrical shape and has an inner peripheral surface 3a. A herringbone-shaped dynamic pressure groove 3a11 is formed on the bearing surface 3a1 of the inner peripheral surface 3a. The dynamic pressure groove 3a11 has a groove depth of several μm, and the shape dimension is finished with high accuracy. A hill portion 3a12 is formed between the dynamic pressure groove 3a11 and the dynamic pressure groove 3a11, and a belt-like portion 3a13 is formed in the center portion in the axial direction (the dynamic pressure groove 3a11 is shown by cross-hatching). With this configuration, when the shaft member 2 rotates, the air is compressed by the dynamic pressure grooves 3a11 and the shaft member 2 floats.

  The bearing sleeve 3 is a CIM molded product having a simple shape without the dynamic pressure groove 3a11 on the bearing surface 3a1 (see FIG. 6). Since the accuracy after firing of the CIM molded product is further improved, the grinding cost of the subsequent process can be kept low, or the grinding can be omitted. Further, the bearing surface 3a1 of the bearing sleeve 3 is provided with a highly accurate dynamic pressure generating groove 3a11 formed by ultrashort pulse laser processing.

  FIG. 3 shows a manufacturing process of the bearing sleeve 3. The manufacturing process of the bearing sleeve 3 includes a CIM process including injection molding, degreasing, and sintering of a ceramic compound, and the dynamic pressure groove 3a11 is formed in the ceramic sintered body 3b (see FIG. 6) of the bearing sleeve manufactured thereby. It consists of an ultrashort pulse laser processing process.

  FIG. 4 shows the CIM injection molding process. The ceramic compound M is obtained by kneading ceramic powder and a resin-based binder, and this is injection molded into the mold 8. The mold 8 is constituted by a split mold, for example, and has a cavity 10 in which a middle mold 9 is disposed. A ceramic compound M is injected from the injection nozzle 11 into the cavity 10 and injection molded. The inner peripheral surface of the mold 8 and the outer peripheral surface of the middle mold 9 are cylindrical surfaces, and the molded body that is injection-molded has a cylindrical shape on both the inner and outer peripheral surfaces.

  The type of ceramics constituting the bearing sleeve 3 is not particularly limited, but zirconia, alumina, silicon nitride, silicon carbide, and alumina nitride are exemplified from the viewpoint of wear resistance. Among these, zirconia is preferable because it has higher mechanical strength than other ceramics and is excellent in toughness. In addition, since zirconia has a linear expansion coefficient almost equal to that of metal, even if the other member (eg shaft member) is made of a metal member, the change in the bearing gap due to temperature change is small. Is possible.

  In CIM, ceramics have a high hardness, and therefore, a hard film having a surface hardness higher than that of ceramics may be applied to the mold 8 and the middle mold 9 as a countermeasure against wear of the mold 8 and the middle mold 9. For example, when zirconia (about Hv 1300) is used as the ceramic constituting the bearing sleeve 3, titanium nitride (TiN: Hv 2000 to 3000) or diamond-like carbon (DLC: DLC: surface treatment to the mold 8 and the middle mold 9 is used. Hv1000-8000), chromium nitride (CrN: Hv2000-2200), etc. are processed.

  The molded body is taken out from the mold 8 and the middle mold 9 and placed in a sintering furnace to be degreased and sintered. Thereby, the ceramic sintered body 3b (refer FIG. 6) by CIM of a bearing sleeve is obtained. The dynamic pressure grooves 3a11 are not yet formed on the inner peripheral surface of the ceramic sintered body 3b.

In order to confirm the accuracy of the ceramic sintered body 3b of the bearing sleeve, the result of the molding test is as follows. The molded sample is a bottomed cylinder having an inner diameter of 4.0 mm, an outer diameter of 9.5 mm, a width of 7.57 mm, and a bottom thickness of 1.5 mm.
〔test results〕
Sample 1: 2 μm inside diameter and 2 μm outside diameter
Sample 2: Inner diameter is 2 μm, Outer diameter is 7 μm
Sample 3: 1 μm inside diameter and 4 μm outside diameter
Sample 4: 1 μm inside diameter and 1 μm outside diameter
Sample 5: inner diameter is 2 μm, outer diameter is 1 μm
It was found that the diameter difference of the ceramic sintered body 3b by CIM is about 7 μm at the maximum, and a highly accurate perfect circular shape can be obtained with a grinding allowance of about several μm.

  Next, the ultrashort pulse laser processing of the dynamic pressure groove 3a11 will be described with reference to FIG. The dynamic pressure groove 3a11 is formed by a series of laser beam spots 12 using an ultrashort pulse laser. This ultrashort pulse laser is a Q-switched YAG laser with a pulse width of 1 ns to 100 ns, and any of the fundamental wave (wavelength 1064 nm), second harmonic (wavelength 532 nm) and third harmonic (wavelength 355 nm) of this YAG laser. Use one. FIG. 5 shows an example of machining the herringbone-shaped dynamic pressure groove 3 a 11 of the bearing sleeve 3. A laser beam spot 12 is applied along the inclined shape of the dynamic pressure groove 3a11 while giving rotation and axial movement to the bearing sleeve 3, and the dynamic pressure groove 3a11 is processed by a series of continuous hit points. In the above processing example, an ultrashort pulse laser with a fundamental wave (wavelength of 1064 nm) is used. However, the invention is not limited to this, and an ultrashort pulse with a shorter second wave (wavelength of 532 nm) or third harmonic wave (wavelength of 355 nm) is used. Lasers can also be used.

During processing by the continuous dotting the laser beam spot 12, as the energy density of the laser, the range of 1GW / cm ² ~40GW / cm ² are particularly good. If the power density is less than 1 GW / cm ² , the metal or ceramic surface cannot be ablated instantaneously, and the processing efficiency is significantly reduced. If the power density is higher than 40 GW / cm ² , the quality deteriorates due to the remaining heat-affected layer or the occurrence of burrs on the processed surface.

  Further, since the processing surface (bottom surface of the groove) of the dynamic pressure groove 3a11 depends on the shape of the energy density distribution of the laser, the laser beam spot 12 is oscillated (in order to improve the flatness of the groove bottom). It is better to process the dynamic pressure groove 3a11 while swinging. Considering the processing efficiency at this time, the diameter of the laser beam spot 12 is particularly preferably in the range of 1/10 to 1/2 of the width of the dynamic pressure groove 3a11.

  Further, at the time of laser processing, the laser beam irradiation direction may be inclined with respect to a line perpendicular to the processing surface of the workpiece. As a result, the gasified / plasmaized ceramic is less likely to adhere to the optical system, and a decrease in laser energy density and beam accuracy due to contamination of the optical system can be suppressed.

  The gasified / plasmaized material irradiated with the laser is reattached (condensed) to the CIM molded product 3b ceramic sintered body of the bearing sleeve, which is a workpiece, and causes projections and burrs. Therefore, it is desirable to process while spraying water or gas so that the gasified / plasmaized ceramic does not adhere to the bearing sleeve 3. In particular, since the second or third harmonic laser can process the bearing sleeve 3 without being absorbed by water, the workpiece of the bearing sleeve or the shaft member is placed in the water during the laser processing. Alternatively, if the workpiece is processed with running water, high-quality dynamic pressure groove processing is possible without reducing the processing efficiency.

  The irradiation point of the ultrashort pulse laser is removed by gasifying and plasmaizing the extreme surface layer of 1 to 4 μm instantaneously (on the order of nanoseconds) to 5000 ° C. or more. Since the temperature rise rate is very fast and is instantaneously gasified and plasma removed, the heat conduction in the ceramic sintered body 3b of the target bearing sleeve is minimized, and as a result, the heat-affected layer Is minimized.

  FIG. 6 shows a processing flow of the bearing sleeve 3. In this flow, after forming, degreasing, and sintering by CIM, the process of grinding the ceramic sintered body 3b of the bearing sleeve is performed, and the dynamic pressure groove 3a11 is laser processed. However, grinding may be performed after laser processing of the dynamic pressure groove 3a11. Further, when the diameter difference of the ceramic sintered body 3b of the bearing sleeve is extremely small, it is possible to eliminate the grinding process.

  7 and 8 show a bearing sleeve 23 used in the second embodiment of the present invention. The bearing sleeve 23 has a spiral dynamic pressure groove 23c11 formed on an end surface 23c. The spiral-shaped dynamic pressure groove 23c11 functions as a thrust bearing. Although the bearing sleeve 23 shown in FIG. 7 and FIG. 8 is illustrated in which a dynamic pressure groove is not formed on the inner peripheral surface 23a, it is the same as the inner peripheral surface 3a of the bearing sleeve 3 used in the first embodiment. The dynamic pressure groove 3a11 may be formed. In this case, the bearing sleeve 23 has both functions of a radial bearing and a thrust bearing.

  The hydrodynamic bearing device in which the bearing sleeve 23 is used has a form similar to the hydrodynamic bearing device 31 of the third embodiment described later. By replacing the bearing sleeve 23 with the rotating sleeve 33 shown in FIG. 9, the dynamic pressure groove of the thrust bearing portion 36a of the base 34 can be omitted. Illustration is omitted.

  FIG. 8 shows the manufacturing process of the bearing sleeve 23. The CIM process in the manufacturing process of the bearing sleeve 23, the hard coating treatment of the CIM molding die, the ceramic type of the bearing sleeve 23, the laser processing of the dynamic pressure groove 23a11, and Since the necessity of grinding is the same as that of the bearing sleeve 3 used in the first embodiment, description thereof is omitted.

  9 to 11 show a third embodiment. As shown in FIG. 9, in the hydrodynamic bearing device 31, the shaft member 32 is fastened and fixed to the base 34 by screws 37. The rotating sleeve 33 is fitted on the shaft member 32. The shaft member 32 has a herringbone-shaped dynamic pressure groove 32a11 formed on the bearing surface 32a1 of the outer peripheral surface 32a thereof. A radial gap 35 is formed between the bearing surface 32 a 1 of the outer peripheral surface 32 a of the shaft member 32 and the inner peripheral surface 33 a of the rotary sleeve 33. In order to support the axial load, the end surface 33 b of the rotating sleeve 33 is disposed to face a thrust bearing portion 36 a formed on the upper surface of the base 34. Although illustration is omitted, a dynamic pressure groove is also formed in the thrust bearing portion 36a. In this dynamic pressure bearing device 31, the shaft member 32 is a fixed type, and a rotating sleeve 33 fitted on the shaft member 32 is rotatable. The rotating sleeve 33 is connected to a rotor of a motor (not shown), and rotates a rotating body (indicated by a two-dot chain line) such as a polygon mirror of a laser beam printer attached to the rotating sleeve 33. FIG. 9 shows a state in which the rotating sleeve 33 is rotating. The rotating sleeve 33 is lifted by the dynamic pressure action of air generated in the radial gap 35 and the thrust gap 38, and the upper surfaces of the shaft member 32 and the base 34 are shown. Is supported in a non-contact state. Also in this embodiment, the radial gap 35 and the thrust gap 38 are exaggerated for easy understanding.

  FIG. 10 shows a shaft member 32 which is a component of the third embodiment. The shaft member 32 is formed in a cylindrical shaft shape and has an outer peripheral surface 32a. A herringbone-shaped dynamic pressure groove 32a11 is formed on the bearing surface 32a1 of the outer peripheral surface 32a. The dynamic pressure groove 32a11 has a groove depth of several μm, and the shape and dimension are finished with high accuracy. A hill portion 32a12 is formed between the dynamic pressure groove 32a11 and the dynamic pressure groove 32a11, and a belt-like portion 32a13 is formed at the center in the axial direction (the dynamic pressure groove 32a11 is indicated by cross-hatching). With this configuration, when the rotating sleeve 33 rotates, air is compressed by the dynamic pressure groove 32a11 and the rotating sleeve 33 rises.

  The manufacturing process of the shaft member 32 is similar to the bearing sleeve 3 which is a component of the first embodiment. The CIM process includes injection molding, degreasing, and sintering of a ceramic compound, and the shaft member ceramics manufactured thereby. It consists of an ultrashort pulse laser processing step for forming a dynamic pressure groove 32a11 in the sintered body 32b (see FIG. 11).

  The shaft member 32, which is a component of the third embodiment, is also a ceramic sintered body 32b having a simple shape without the dynamic pressure groove 32a11 on the bearing surface 32a1. Therefore, since the accuracy of the ceramic sintered body 32b is further improved, the grinding cost of the post-process can be kept low, or the grinding can be omitted. In addition, the bearing surface 32a1 of the shaft member 32 is provided with a high-precision dynamic pressure groove 32a11 formed by ultrashort pulse laser processing.

  FIG. 11 shows a processing flow of the shaft member 32. In this flow, after forming, degreasing, and sintering by CIM, the process of grinding the ceramic sintered body 32b is performed, and the dynamic pressure groove 32a11 is laser processed. However, as described in the first embodiment, the grinding process may be performed after the laser processing of the dynamic pressure groove 32a11, and if the diameter difference of the ceramic sintered body 32b is extremely small, the grinding process is not necessary. Is also possible.

  The CIM process in the manufacturing process of the shaft member 32, the hard film treatment of the CIM molding die, the ceramic type of the shaft member 32, the laser processing of the dynamic pressure groove 32a11, etc. are all bearings that are constituent parts of the first embodiment. Since it is the same as that of the sleeve 3, the detailed description is omitted.

  FIG. 12 shows a bearing sleeve 43 which is a component of the fourth embodiment. The bearing sleeve 43 has a bottom 43c at one end of a cylindrical portion 43d. A spiral dynamic pressure groove 43c11 is formed on the upper surface of the bottom 43c.

  Since the hydrodynamic bearing device using the bearing sleeve 43 has a form similar to the hydrodynamic bearing device 1 of the first embodiment, the illustration thereof is omitted. In addition, the CIM process in the manufacturing process of the bearing sleeve 43, the hard film treatment of the CIM molding die, the ceramic type of the bearing sleeve 43, the necessity of laser processing and grinding of the dynamic pressure groove 43c11, etc. Since it is the same as that of the bearing sleeve 3 which is the component of embodiment, description is abbreviate | omitted.

  The dynamic pressure groove formed in the bearing sleeve or the shaft member which is a component of each embodiment is not limited to a herringbone shape or a spiral shape. Not limited to this, dynamic pressure is generated by forming other types of dynamic pressure grooves, for example, by forming the inner peripheral surface of the bearing sleeve and the outer peripheral surface of the shaft member into a multi-arc shape combining a plurality of arcs. You may comprise a part.

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 2a Outer peripheral surface 2a1 Bearing surface 2b End surface 3 Bearing sleeve 3a Inner peripheral surface 3a1 Bearing surface 3a11 Dynamic pressure groove 3a12 Hill part 3a13 Band-shaped part 3b Ceramic sintered body 4 CIM 4 Housing 4a Bottom part 4b Thrust bearing Part 5 Radial gap 6 Thrust gap 8 Mold 9 Middle mold 10 Cavity 11 Injection nozzle 12 Beam spot 23 Bearing sleeve 23a Inner peripheral surface 23b Ceramic sintered body 23c by CIM End face 23c11 Dynamic pressure groove 31 Dynamic pressure bearing device 32 Shaft member 32a Outer peripheral surface 32a1 Bearing surface 32a11 Dynamic pressure groove 32a12 Hill 32a13 Band-shaped portion 32b Ceramic sintered body 33 by CIM Rotating sleeve 33a Inner peripheral surface 33b End surface 34 Base 35 Radial clearance 36a Thrust bearing portion 37 Screw 38 Thrust clearance 43 Bearing three 43c bottom 43c11 dynamic pressure grooves 43d cylindrical portion M ceramic compound

Claims (22)

  In a hydrodynamic bearing device having a bearing sleeve or a shaft member in which a dynamic pressure groove is formed on the bearing surface, the bearing sleeve or the shaft member is a ceramic injection molded product having a shape having no dynamic pressure groove on the bearing surface. A hydrodynamic bearing device comprising hydrodynamic grooves formed by ultrashort pulse laser processing on the bearing surface.   The hydrodynamic bearing device according to claim 1, wherein a bearing surface of the bearing sleeve or the shaft member is finished by grinding.   The hydrodynamic bearing device according to claim 1 or 2, wherein the ceramic material of the bearing sleeve or the shaft member is zirconia.   The hydrodynamic bearing device according to any one of claims 1 to 3, wherein the hydrodynamic groove is machined by continuous hitting points using an ultrashort pulse laser.   5. The hydrodynamic bearing device according to claim 1, wherein a pulse width of the ultrashort pulse laser is 1 to 100 ns.   The hydrodynamic bearing device according to claim 1, wherein a bearing surface of the bearing sleeve is at least one of an inner peripheral surface and an end surface.   The hydrodynamic bearing device according to claim 1, wherein a bearing surface of the shaft member is at least one of an outer peripheral surface and an end surface.   The hydrodynamic bearing device according to claim 6 or 7, wherein the hydrodynamic groove formed in the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member has a herringbone shape.   8. The hydrodynamic bearing device according to claim 6, wherein the hydrodynamic groove formed on the end surface of the bearing sleeve or the shaft member has a spiral shape.   The hydrodynamic bearing device according to claim 1, wherein the bearing sleeve has a bottom portion, and a bearing surface of the bearing sleeve is at least one of an inner circumferential surface and a top surface of the bottom portion. .   The hydrodynamic bearing according to claim 10, wherein the hydrodynamic groove formed on the inner peripheral surface of the bearing sleeve has a herringbone shape, and the hydrodynamic groove formed on the upper surface of the bottom portion has a spiral shape. apparatus.   The hydrodynamic bearing device according to any one of claims 1 to 11, wherein the hydrodynamic bearing device supports a bearing sleeve or a shaft member by a hydrodynamic action of air.   In a method of manufacturing a hydrodynamic bearing device having a bearing sleeve or a shaft member in which a dynamic pressure generating groove is formed on the bearing surface, the bearing sleeve or the shaft member is formed into a shape having no dynamic pressure groove on the bearing surface by ceramic injection molding. And a method of manufacturing a hydrodynamic bearing device, comprising: a degreasing and sintering step; and a step of forming a hydrodynamic groove on the bearing surface by an ultrashort pulse laser.   14. The method for manufacturing a hydrodynamic bearing device according to claim 13, further comprising a step of grinding the bearing surface as a step of manufacturing the bearing sleeve or the shaft member.   14. The method of manufacturing a hydrodynamic bearing device according to claim 13, wherein the hydrodynamic groove is processed by continuous hitting with an ultrashort pulse laser. As the ultrashort pulse laser, any one of a fundamental wave, a second harmonic wave, and a third harmonic wave of an ultrashort pulse Q-switched YAG laser having a pulse width of 1 ns to 100 ns is used. the laser power density to a value in the range of ^{1GW / cm 2 ~100GW / cm 2} , the dynamic pressure bearing device according to claim 15, characterized in that the diameter of the beam spot of the laser is made smaller than the width of the dynamic pressure grooves Manufacturing method.   The optical system of the beam spot of the laser is oscillated by at least one of electrical control and mechanical control during processing by the continuous hitting point. Manufacturing method of the hydrodynamic bearing device.   In the laser processing, the ceramic sintered body to be processed is disposed in water, or flowing water is applied to the ceramic sintered body, according to any one of claims 13 and 15-17. The manufacturing method of the hydrodynamic bearing apparatus of description.   The laser beam irradiation direction is inclined with respect to a line perpendicular to the processed surface of the ceramic sintered body during the laser processing. A method for manufacturing the hydrodynamic bearing device according to 1.   14. The method for manufacturing a hydrodynamic bearing device according to claim 13, wherein the ceramic injection mold is provided with a hard coating having a hardness equal to or higher than the hardness of the ceramic material of the molded product.   21. The hydrodynamic bearing device according to claim 20, wherein the hard coating is a hard coating selected from titanium nitride (TiN), diamond-like coating (DLC), and chromium nitride (CrN). Production method.   The bearing sleeve or shaft member based on the manufacturing method of the hydrodynamic bearing apparatus of any one of Claims 13-21.

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