JP5320045B2 - Fluid dynamic pressure bearing manufacturing method, fluid dynamic pressure bearing, and disk drive device using the same - Google Patents

Description

  The present invention relates to a manufacturing method of a fluid dynamic pressure bearing, a fluid dynamic pressure bearing, and a disk drive device including the fluid dynamic pressure bearing.

  In recent years, disk drive devices such as HDDs have been provided with fluid dynamic pressure bearings, so that rotational accuracy has been dramatically improved, and high density and large capacity have become possible. For this reason, fluid dynamic pressure bearings and disk drive devices equipped with such fluid dynamic bearings have been installed in various devices. For this reason, the usage environment has become widespread, and improvements in characteristics such as small size, light weight, low current, and high rigidity have been demanded, and provision at a lower cost has been demanded.

  With such diversification of needs, the specifications of the disk drive device have diversified, and various specifications have been required for the fluid dynamic pressure bearings mounted on the disk drive apparatus. Therefore, it is required to efficiently produce a wide variety.

  In order for the disk drive device to be driven stably, the built-in fluid dynamic pressure bearing needs to exhibit a predetermined performance and smoothly rotate the rotating shaft. For this purpose, a fluid dynamic pressure bearing suitable for use in a disk drive device is required. In a general disk drive device, a rotary shaft is stored in a space surrounded by a sleeve and other members, and the storage space is filled with a lubricant. Further, herringbone-shaped dynamic pressure grooves are provided in a plurality of portions that are axially separated on the inner periphery of the sleeve. When the rotating shaft rotates and the lubricant flows into the herringbone-shaped dynamic pressure groove, a high pressure portion is generated in the lubricant. The rotary shaft is separated from the surrounding wall surface by the pressure, and the rotary shaft is rotated in a substantially non-contact manner. As a result, stable high-speed rotation of the recording disk rotated by the rotating shaft is realized, and stable data writing or reading is executed.

The sleeve having such a dynamic pressure groove is processed by, for example, a groove processing tool having a rolled ball. In other words, the groove processing tool is inserted into the cylindrical portion of the bearing base material that becomes the sleeve, and processing is performed while pressing a plurality of rolling balls embedded at the tip of the groove processing tool against the inner peripheral surface of the bearing base material. Thus, herringbone-shaped dynamic pressure grooves are sequentially formed (see, for example, Patent Document 1 and Patent Document 2).
JP-A-10-76411 Japanese Patent Laid-Open No. 11-19804

  In the ball rolling process as described above, the shape dimension of the bottom of the dynamic pressure groove is determined by the distance from the center of the outer peripheral tip of the ball of the groove processing tool. For this reason, when the radius of the shaft housing hole portion of the bearing base material changes, the change in the radius directly changes the dynamic pressure groove depth. As a result, there is a problem that the dynamic pressure generated by such a dynamic pressure groove also changes and the dynamic pressure balance is not as designed.

  In addition, there is a problem that cannot be coped with when the dynamic pressure groove depth is to be adjusted according to the distance from the end of the shaft housing hole. In addition, since ball rolling cannot be processed at high speed, it takes time to process, and the stress applied to the bearing base material during processing is likely to cause deformation of the bearing base material, resulting in a decrease in dimensional accuracy of the sleeve after processing. There was also.

  Furthermore, it is difficult to set the ball radius of general ball rolling to R 0.3 mm or less. For this reason, it was not possible to create a fine shape of R 0.3 mm or less as the dynamic pressure groove shape. Further, since the grooving tool is dedicated depending on the machining diameter, if the machining diameter is different even at 1 μm, another grooving tool must be made. For example, in a bearing for a 2.5 inch hard disk drive device, the inner diameter of the cylindrical portion is 2.5 mm, and an inner diameter of the cylinder portion for a 3.5 inch inch hard disk drive device is 4.0 mm. Therefore, it was necessary to prepare a dedicated grooving tool and equipment for using it. As a result, it is uneconomical in terms of cost and resources, and has become a major problem. Furthermore, if it is attempted to change the inner diameter of the cylindrical portion even if it is only 1 μm for some reason, there has been a problem that a grooving tool must be newly constructed and the equipment must be modified.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of manufacturing a fluid dynamic bearing capable of meeting various dimensional requirements. Another object of the present invention is to provide a fluid dynamic pressure bearing manufactured using the method of manufacturing the fluid dynamic pressure bearing and a disk drive device including the fluid dynamic pressure bearing.

  In order to solve the above-described problem, an aspect of the present invention is configured to support a bearing base material having a housing hole portion of a rotating shaft at the center and rotate the bearing base material around the central axis to thereby store the housing. A fluid dynamic pressure bearing manufacturing method in which a dynamic pressure groove is formed by cutting an inner surface of a hole portion with a cutting tool, and is fine in a second processing direction perpendicular to the first processing direction along the central axis of the bearing base material. A linear groove having a length corresponding to the circumferential width of the dynamic pressure groove formed on the inner peripheral surface of the storage hole portion by the cutting tool that is driven alternately is along the circumferential direction of the surface orthogonal to the first machining direction. Forming a linear groove, and displacing the relative position of the bearing base material and the cutting tool in the first processing direction to continuously form the linear groove in the first processing direction. Extending a dynamic pressure groove extending in the direction. It is characterized in.

  According to this aspect, the circumferential width of the dynamic pressure groove formed on the inner peripheral surface of the storage hole by the cutting tool that is micro-alternatively driven in the second machining direction perpendicular to the first machining direction along the central axis of the bearing base material Are formed along the circumferential direction of the surface perpendicular to the first processing direction. And this linear groove | channel is continuously formed in a 1st process direction, and the dynamic pressure groove extended in the said 1st process direction is extended. At this time, the groove depth can be changed by controlling the drive amount of the cutting tool that is driven in a minute alternating manner in the second machining direction. That is, even when the radius of the storage hole changes, the change can be easily followed, and a dynamic pressure groove having a constant depth or a desired depth can be formed. Moreover, since it is a cutting process by a cutting tool, an increase in machining resistance can be suppressed, and the machining resistance can be further adjusted by adjusting the cutting depth as necessary, so that deformation of the bearing base material can be suppressed. Further, the length of the linear groove formed along the circumferential direction of the surface orthogonal to the first machining direction can be determined without changing the relative position of the bearing base material and the cutting tool in the first machining direction. The width of the pressure groove can be easily changed. Therefore, even when the radius of the storage hole changes, or when the width or depth of the dynamic pressure groove is changed, the dynamic pressure groove can be processed using the same cutting tool. Further, since the radius of the tip shape of the cutting tool can be made sufficiently smaller than the ball radius of ball rolling, it is possible to easily form a dynamic pressure groove having a finer shape than ball rolling.

  In the above aspect, the storage hole has a tapered shape in which both end sides of the bearing base material are smaller in diameter than the inner side, and the cutting tool has the second machining direction according to a displacement amount and a taper angle in the first machining direction. You may make it adjust the depth of the dynamic pressure groove extended by changing the amplitude amount at the time of the alternating drive to.

  In the cylindrical fluid dynamic pressure bearing, the inner peripheral surface of the bearing hole of the bearing base material has a taper that is narrow at both ends and increases in radius toward the center for the purpose of preventing the intermediate portion from being below atmospheric pressure. It is desirable. According to this aspect, even when the inner peripheral surface of the storage hole portion is tapered, the depth of the dynamic pressure groove can be easily adjusted following the tapered shape by changing the amplitude amount during the alternating drive.

  In the above aspect, the storage hole has a tapered shape in which both end sides of the bearing base material are smaller in diameter than the inner side, and the cutting tool is placed on a tool table movable in the second processing direction. The table may adjust the depth of the dynamic pressure groove extending by moving the cutting tool in the second processing direction in accordance with the amount of movement in the first processing direction and the taper angle.

  Since the cutting tool is mounted on a tool table that can move in the second machining direction, even when the taper angle is large, the cutting tool can be moved quickly according to the inner diameter of the storage hole, improving machining efficiency. Can contribute. Further, even when the inner diameter of the storage hole changes greatly, the cutting tool can be moved quickly, so that it is possible to easily cope with processing of the storage hole of various dimensions.

  In the above aspect, the radius of the tip of the cutting tool may be 0.02 mm to 0.1 mm. The displacement amount of the tool table in the second processing direction may be 1.0 mm or more. By processing at such a set value, a highly accurate fluid dynamic pressure bearing can be efficiently processed and manufactured.

  In order to solve the above problems, according to another aspect of the present invention, a rotating shaft, a shaft storing member that rotatably stores the rotating shaft, and an axially spaced apart inner circumferential surface of the shaft storing member are arranged. A first radial dynamic pressure groove and a second radial dynamic pressure groove provided; a circumferential recess disposed between the first radial dynamic pressure groove and the second radial dynamic pressure groove; and the rotary shaft. A fluid dynamic pressure bearing provided with a lubricant filled in a gap between the outer peripheral surface of the shaft housing member and the inner peripheral surface of the shaft housing member, wherein the first radial dynamic pressure groove and the second radial dynamic pressure groove are: A linear groove formed along the circumferential direction of the surface orthogonal to the axial direction and having a length corresponding to the circumferential width of the dynamic pressure groove is continuously arranged in the axial direction on the inner circumferential surface of the shaft housing member. It is characterized by becoming.

  According to this aspect, the first radial dynamic pressure groove and the second radial dynamic pressure groove have a length corresponding to the circumferential width of the dynamic pressure groove on the inner peripheral surface of the shaft housing member, and the circumference of the surface orthogonal to the axial direction. Since the linear groove formed along the direction is continuously arranged in the axial direction, it is possible to provide a fluid dynamic pressure bearing capable of setting the width dimension of the dynamic pressure groove by setting the length of the linear groove. Moreover, the fluid dynamic pressure bearing which can set the depth of a linear groove easily can be provided.

  In the above aspect, the first radial dynamic pressure groove and the second radial dynamic pressure groove may have a herringbone shape of 3 μm to 8 μm. The curvature radius of the bent portion of the first radial dynamic pressure groove and the second radial dynamic pressure groove of the herringbone shape may be 0.02 mm to 0.1 mm. The inner diameter of the shaft housing member may be 2 mm to 4 mm. Moreover, the thickness of the site | part which forms the dynamic pressure groove of the said shaft storage member may be 0.2 mm-0.6 mm. Moreover, the taper which a diameter expands toward an intermediate part from the edge part may be formed in the internal peripheral surface of the said shaft storage member. The first radial dynamic pressure groove and the second radial dynamic pressure groove may have a herringbone shape, and the dynamic pressure groove depth of the bent portion may be shallower than the dynamic pressure groove depth of other portions.

  In the above aspect, a rectifying blade may be formed on the bottom surface of the dynamic pressure groove along the circumferential direction of the shaft housing member. The bottom surface of the dynamic pressure groove surface formed by ball rolling has a smooth surface and a small contact angle with the lubricant on the surface. As a result, the resistance due to the viscosity of the lubricant increases, leading to an increase in rotational load, and there is a problem that leads to an increase in current for rotating the rotating shaft. By forming the rectifying blades along the circumferential direction of the shaft housing member, the contact angle of the bottom surface of the dynamic pressure groove with the lubricant can be increased. As a result, the substantial viscosity of the lubricant on the bottom surface of the dynamic pressure groove can be reduced, so that the rotational load can be reduced and the current can be reduced. Note that the rectifying blade may be cut out exclusively, or may be substituted by a so-called catch (blade mark) formed by adjusting the radius of the cutting tool tip and the feed pitch.

  If the fluid dynamic pressure bearing in the above aspect is used, disk drives of various specifications can be easily provided.

  According to the present invention, the shape of the dynamic pressure groove can be freely created with a fine shape that has not been conventionally provided, and it can contribute to the improvement of accuracy and performance of the dynamic pressure groove. Also, fluid dynamic pressure bearings with different specifications can be produced efficiently.

  FIG. 1 is an explanatory diagram of a manufacturing apparatus 10 used in a fluid dynamic bearing manufacturing method according to an embodiment of the present invention. A rotation drive unit 14 is disposed on the base 12. The rotation drive unit 14 rotates a bearing base material (hereinafter referred to as “work 16”) that forms a sleeve functioning as a shaft housing member that houses a rotating shaft of a fluid dynamic pressure bearing by a chuck 18. For example, about 3000 rotations per minute is selected as the rotation speed of the rotation drive unit 14. This is a value selected based on a test result that there is a problem that the machining time becomes long when the rotation is 1000 rotations per minute or less, and there is a problem that the machining accuracy is deteriorated when the rotation exceeds 5000 rotations per minute. However, it is desirable to change the rotation speed as appropriate by changing the material and size of the workpiece, the processing conditions, and the like.

  FIG. 2 is a top view for explaining the work 16 and a tool mounting portion 22 that holds the tool 20 as a cutting tool. The tool mounting portion 22 is arranged so that the tool 20 is positioned on the extension of the rotation center of the work 16. At this time, the rotation center of the workpiece 16 is defined as a Z-axis direction (also referred to as a first machining direction), and a direction orthogonal to the Z-axis direction is defined as an X-axis direction (also referred to as a second machining direction).

  In the manufacturing apparatus 10, at least one of the rotation drive unit 14 or the tool mounting unit 22 moves in the Z-axis direction. Further, a first X-axis drive unit 24 for finely moving the tip of the cutting tool 20 in the X-axis direction (second processing direction), and a second X-axis drive for mounting and moving the tip 20 in the X-axis direction (second processing direction) A portion 26 is provided. The second X-axis drive unit 26 can use a servo motor or the like as its drive source.

  In the present embodiment, as shown in FIG. 2, the first X-axis drive unit 24 uses a piezoelectric element 28 as a drive source. The maximum response speed of the first X-axis drive unit 24 is, for example, 1 kHz, the resolution is 0.1 μm, and the amplitude is 10 μm. The first X-axis drive unit 24 includes a capacitance type displacement sensor 30 that detects the drive displacement of the piezoelectric element 28. By feeding back the output of the displacement sensor 30, the piezoelectric element 28 is accurately driven, and the temperature characteristics of the piezoelectric element 28 are improved to enhance response performance and displacement accuracy, thereby enabling high-precision machining.

  In this embodiment, a rotation reference position detection unit (not shown) that detects the rotation reference position of the workpiece 16, an encoder (not shown) that detects the rotation angle of the workpiece 16, and a bite position detection unit that detects the position of the bite. (Not shown) and a control unit (not shown) that controls the alternating cycle and phase of the piezoelectric element 28 according to the outputs of the rotation reference position detection unit, the encoder, and the bite position detection unit. The rotation reference position detection unit may be configured to count the output signal of the encoder and detect the rotation reference position of the workpiece 16 for each rotation.

  Various drive waveforms such as a substantially rectangular wave shape and a substantially sine wave shape have been tried as the drive voltage waveform of the first X-axis drive unit 24, but a test result that provides a preferable machining accuracy is obtained with a drive waveform having a substantially sine wave shape or a substantially trapezoidal wave shape. It was. For example, in the case of a substantially sinusoidal driving voltage waveform as shown in FIG. 3, the tip of the cutting tool 20 is not cut away from the surface of the workpiece 16 in one half cycle, and is cut in the other half cycle. . The position of the first X-axis drive unit 24 configured as described above is adjusted by the second X-axis drive unit 26. As a result, it is possible to cut only the portion of the dynamic pressure groove without cutting the entire circumference of the inner surface of the workpiece 16, and it is possible to provide preferable processing accuracy. Further, since the contact state of the cutting tool 20 with respect to the workpiece 16 can be optimized, the tool wear characteristic can be improved. The manufacturing apparatus 10 is connected to a pulse transmitter 32 and a piezoelectric element driving power source 34 for driving the piezoelectric element 28, and executes feedback control for driving the piezoelectric element 28 in an optimum state. A displacement sensor controller 36 and the like are connected.

  The inner peripheral surface of the shaft housing hole of the workpiece 16 of the present embodiment has a taper whose both ends are narrow and the radius increases toward the center. This taper is provided for the purpose of preventing the intermediate portion from becoming below atmospheric pressure when the fluid dynamic pressure bearing functions. In this embodiment, the diameter is increased by about 0.6 μm at the center relative to both ends. This taper is formed.

  In the present embodiment, as described above, the second X-axis drive unit 26 is provided separately from the first X-axis drive unit 24. The second X-axis drive unit 26 adjusts the drive position when driving the tip of the cutting tool 20 in the X-axis direction with respect to the inner peripheral surface of the work 16 so as to correspond to the tapered shape described above. Thus, by providing the second X-axis drive unit 26 separately from the first X-axis drive unit 24 and manufacturing the fluid dynamic pressure bearing, a dynamic pressure groove having a constant depth is formed regardless of the presence of the taper. It is possible to stabilize the balance of the generated dynamic pressure. It is also easy to adjust the dynamic pressure groove depth according to the distance from the end of the shaft housing hole. For example, when two herringbone-shaped dynamic pressure grooves are formed along the axial direction (Z-axis direction) of the sleeve, the center side of each dynamic pressure groove is shallower than the portion near the end of the sleeve accommodation hole. By doing so, the suction pressure on the side close to the end becomes relatively high. As a result, the pressure concentrates on the middle part of the sleeve, and it is possible to maintain the atmospheric pressure or higher.

  FIG. 4 is an explanatory diagram schematically showing the relationship between the workpiece 16 and the byte 20. By the alternating control of the piezoelectric elements 28, the tip of the cutting tool 20 operates so as to come into contact with the inner peripheral surface 16a of the cylindrical portion of the rotating workpiece 16 and cut with a cutting depth of a predetermined depth. At this time, since the workpiece 16 is rotating at a high speed and the cutting tool 20 is vibrated by the fine alternating drive of the piezoelectric element 28, the cutting is substantially a point shape.

  FIG. 5A schematically shows the inner peripheral surface 6a of the work 16 developed on a plane in order to explain the process of forming the herringbone-shaped dynamic pressure groove 38 in this embodiment. In FIG. 5A, the locus of the tip of the cutting tool 20 is indicated by a circle. One end of the cutting tool 20 is fixed in the Z-axis direction (first processing direction) of the workpiece 16 to form a single linear groove. That is, the workpiece 16 is rotated and the piezoelectric element 28 is driven in a minute alternating manner to perform cutting on the same inner peripheral surface in the X-axis direction of the workpiece 16, and a length corresponding to the circumferential width t of the dynamic pressure groove 38. A linear groove 40 is formed. For example, when the four dynamic pressure grooves 38 are formed on the inner peripheral surface 16a, point-shaped cutting is performed at four locations by one rotation of the workpiece 16, as described above. Then, while maintaining the relative position of the workpiece 16 and the bit 20 in the Z-axis direction, the rotational cycle of the workpiece 16 and the alternating cycle of the piezoelectric element 28 are slightly shifted so that the point-shaped cutting is performed in the axial direction of the workpiece 16 (Z-axis). It becomes the linear groove | channel 40 of the circumferential direction width t continuous along the circumferential direction of the surface orthogonal to a direction. As another method, the period of micro alternating drive of the piezoelectric element 28 is adjusted, and the linear groove 40 having a length corresponding to the circumferential width t is formed by one contact between the workpiece 16 and the cutting tool 20. Also good. Further, the linear groove 40 having a depth corresponding to the depth of the dynamic pressure groove 38 formed by this one-time contact may be formed, or the dynamic pressure groove 38 while gradually digging in the X-axis direction at the same position. You may form the linear groove | channel 40 of the depth corresponding to this depth. If the linear groove 40 can be formed on the same inner peripheral surface of the surface orthogonal to the Z-axis direction of the workpiece 16, the relative position of the workpiece 16 and the bite 20 in the Z-axis direction (first processing direction) is changed to change the cylindrical portion. The linear groove 40 is formed on the inner peripheral surface 16a so as to be continuously arranged in the Z-axis direction, thereby forming the dynamic pressure groove 38.

  In FIG. 5 (a), the part indicated by a round solid line drives the cutting tool 20 outward in the radial direction of the workpiece 16 in the X-axis direction to start cutting the inner wall, and the cutting part 20 is cut so as not to be cut at the part indicated by the round broken line. Is driven radially inward of the workpiece 16. In the cutting method of the present embodiment, the cutting and non-cutting cycle operations are alternately repeated on the inner peripheral surface along the rotation direction of the workpiece 16. The cutting and non-cutting cycle operations are driven by the first X-axis drive unit 24. This process is called a linear groove forming process. This linear groove forming step can be realized by an electromagnetic driving principle such as a voice coil or a mechanical driving principle such as a cam or hydraulic pressure instead of the piezoelectric element 28, but is not limited thereto. It is to be noted that a highly precise dynamic pressure groove can be formed by controlling the rotation position of the workpiece 16 or the position of the cutting tool 20 in synchronism with the cycle and phase of the alternation instead of simply driving them alternately.

  FIG. 5B shows a step of forming a linear groove 40 along the circumferential direction of the surface orthogonal to the axial direction by a linear groove forming process in which cutting and non-cutting cycle operations of the cutting tool 20 are alternately performed. It is a perspective view which shows a mode that the dynamic pressure groove | channel 38 is formed by forming the linear groove | channel 40 continuously in an axial direction (1st process direction). This process is called an extending process of extending the dynamic pressure groove extending in the first processing direction by continuously forming the dynamic pressure groove 38.

  The manufacturing method of the fluid dynamic bearing described above has various advantages over the conventional manufacturing method of the fluid dynamic bearing by ball rolling. The manufacturing method of the fluid dynamic pressure bearing of the present embodiment will be described below in comparison with the conventional method.

  As described above, it is desirable to taper the inner diameter of the workpiece 16 so that the intermediate portion does not become atmospheric pressure or less when the fluid dynamic pressure bearing is used. Therefore, in the case of the present embodiment, as shown in FIG. 6, the taper is first processed into a taper shape having a large diameter on the center side with respect to the end side as shown by a dotted line. Next, the dynamic pressure groove 38 is cut with the cutting tool 20. At that time, the first X-axis drive unit 24 decreases the amplitude of the piezoelectric element 28 at the end of the work 16 and gradually increases it toward the center. By making the difference in amplitude equal to the difference between the minimum diameter and the maximum diameter of the taper, the locus of the tip of the cutting tool 20 becomes as shown by the solid line in FIG. That is, if the movement in the X direction is a slight taper angle, the dynamic pressure can be adjusted at any position of the workpiece 16 by adjusting the amplitude of the piezoelectric element 28 without moving the second X-axis drive unit 26 during the dynamic pressure groove processing. The depth of the groove 38 can be made uniform. By controlling the first X-axis drive unit 24 as described above, the shape of the dynamic pressure groove 38 can be finely processed into an arbitrary shape. Moreover, it is easy to change the depth at an arbitrary position of the dynamic pressure groove 38, and fine adjustment of the dynamic pressure performance can be performed.

  By the way, in the conventional dynamic pressure groove processing by ball rolling, the ball radius can be made smaller than the width of the dynamic pressure groove in order to generate a large processing resistance for rolling and to extend the dynamic pressure groove in the groove direction. However, practically, it was not possible to make R 0.3 mm or less. For this reason, the dynamic pressure groove shape could not be made as fine as R 0.3 mm or less. In this embodiment, as shown in FIG. 5A and FIG. 5B, the linear groove 40 is formed in the width direction of the dynamic pressure groove 38 and is continuous. The radius of the tip of the cutting tool 20 can be reduced regardless of the width of the cutting tool 20. When the radius of the tip of the cutting tool 20 is set to R0.1 mm or less, for example, the dynamic pressure groove 38 can be freely formed with a fine shape of R0.1 mm or less. Further, since the cutting resistance can be lowered by reducing the radius of the tip of the cutting tool 20, even a thin workpiece 16 can be easily processed without causing shape deformation. In addition, since the test result that the durability of the cutting tool 20 is reduced when the radius of the tip of the cutting tool 20 is made smaller than R 0.02 mm is obtained, the radius R of the tip of the cutting tool 20 is 0.02 to 0.1 mm. It is desirable to choose between.

  Further, since the conventional ball rolling grooving tool is dedicated depending on the diameter of the inner peripheral surface of the work 16, another grooving tool must be made if the diameter of the inner peripheral surface is different even by 1 μm. For example, in a 2.5-inch HDD bearing, the diameter of the cylindrical portion is 2.5 mm, and the diameter of the cylindrical portion of the 3.5-inch HDD disk drive device is 4.0 mm. As a result, it is impossible to share a grooving tool, and it is necessary to prepare separate facilities and grooving tools. In other words, it was inefficient in terms of both cost and resources, which was a big problem. Further, if it is attempted to change the inner diameter of the cylindrical portion even for a certain reason, it becomes necessary to newly construct a grooving tool and to modify the equipment. On the other hand, in the present embodiment, the driving distance of the second X-axis drive unit 26 that mounts the first X-axis drive unit 24 and drives in the X-axis direction can be 1 mm or more. Therefore, even if the difference in diameter of the inner peripheral surface of the workpiece 16 is 2 mm or more, it can be processed by the same processing apparatus. Since the diameter difference between the inner peripheral surfaces of the bearings for 2.5-inch and 3.5-inch HDDs is 1.5 mm, it can be processed by the same processing apparatus even if the errors of parts and the like are taken into account. For this reason, it is not necessary to prepare multiple types of equipment and grooving tools. Further, even if the inner diameter of the cylindrical portion is changed by a design change, it can be easily handled by the control of the second X-axis drive unit 26, so that there is an advantage that it can easily cope with various dimensions.

  The fluid dynamic pressure bearing manufactured by such a method of manufacturing a fluid dynamic pressure bearing can be easily formed without changing the shape or equipment of the cutting tool 20 so that the shape of the dynamic pressure groove 38 is adapted to the required dynamic pressure characteristics. Can be changed. Therefore, the processing accuracy of the dynamic pressure grooves can be improved as compared with the processing accuracy of the dynamic pressure grooves formed by conventional ball rolling. Therefore, it is possible to provide a fluid dynamic pressure bearing with little variation in characteristics as a bearing. In addition, since a plurality of linear grooves are formed by cutting to form dynamic pressure grooves, the inner periphery is not deformed even with a thin workpiece with little processing stress. Therefore, a small and lightweight fluid dynamic pressure bearing can be provided. Furthermore, since the workpiece can be cut at a high speed, the machining time can be shortened to about 60% of the conventional ball rolling process. As a result, it is possible to provide an inexpensive fluid dynamic pressure bearing that can improve manufacturing efficiency.

  In the case of a conventional fluid dynamic pressure bearing, as shown in FIG. 7, two sets of herringbone-shaped dynamic pressure grooves 38 are formed in the axial direction with the intermediate portion 42 interposed therebetween. In addition, it is designed so that the discharge pressure of the lubricant and the suction pressure are balanced in the fluid dynamic pressure generating portion by the dynamic pressure groove 38. And the intermediate part 42 formed between these fluid dynamic-pressure generation | occurrence | production parts is set to a pressure a little higher than atmospheric pressure. However, in the case of fluid dynamic pressure bearings created by the conventional ball rolling method, the balance between the discharge pressure and the suction pressure tends to be lost due to variations in the inner circumference of the workpiece and the dynamic pressure groove processing, resulting in a pressure at the intermediate portion. It was a cause of inconsistency. When the pressure in the intermediate part becomes below atmospheric pressure due to such variations, the air dissolved in the lubricant is vaporized by the reduced pressure and interposed between the inner peripheral surface and the rotating shaft, resulting in variations in bearing performance. Was one of the causes of

  On the other hand, in the present embodiment, the bearing base material to be the shaft housing portion is formed of, for example, a copper-based material, and the depth of the cylindrical portion with an inner diameter of 2 to 4 mm using the above-described fluid dynamic pressure bearing manufacturing method. Two dynamic pressure grooves 38 having a herringbone shape of approximately 5 μm are formed. FIG. 7 shows a part of a cross section of the workpiece 16, and the inner circumferential surface of the shaft housing hole portion 44 is provided with a taper that extends approximately 0.6 μm in diameter from both ends toward the intermediate portion 42. Yes. By providing this taper, for each of the two sets of dynamic pressure grooves 38 across the intermediate portion 42, the gap between the rotary shaft and the central portion is wider than the portion near the end of the shaft housing hole 44. In this case, the dynamic pressure is such that the suction pressure on the side close to the end where the gap with the shaft is narrow is relatively higher than the central side, and the pressure is concentrated on the intermediate portion 42. As a result, the problem that the intermediate portion 42 is below atmospheric pressure is avoided. In the test, if the difference in diameter due to the taper is smaller than 0.2 μm, the above-mentioned effect due to the pressure concentration cannot be fully expected. On the contrary, if the difference in diameter is larger than 2.0 μm, there may be a problem in the bearing characteristics. Got the result that there is. Therefore, the difference in diameter due to the taper is preferably selected between 0.2 μm and 2.0 μm.

  In a conventional fluid dynamic pressure bearing, when the inner diameter of the cylindrical portion is 2 to 4 mm, there is a demand for reducing the thickness of the portion of the cylindrical portion where the dynamic pressure groove is formed in order to reduce the weight and size of the bearing. For this reason, attempts have been made to roll the ball at a thickness of 1.0 mm or less, for example. However, since the rolling resistance of the ball rolling process is large, the cylindrical part is easily deformed. Therefore, the depth of the dynamic pressure groove is assumed to be shallow not exceeding 3 μm. Also, in the ball rolling process, the variation in the depth of the dynamic pressure groove was large. If the dynamic pressure groove is shallow, the variation in the dynamic pressure due to the variation appears remarkably. As described above, the fluid dynamic pressure bearing produced by ball rolling is liable to cause a reduction in bearing rigidity and non-uniform rotation accuracy, which has been a factor in reducing the performance of equipment equipped with the fluid dynamic pressure bearing.

  On the other hand, in the present embodiment, the bearing base material that becomes the shaft housing hole 44 is formed of, for example, a copper-based material. Further, by using the above-described fluid dynamic pressure bearing manufacturing method, even if the cylindrical portion has an inner diameter of 2 to 4 mm and the thickness of the cylindrical portion of the portion forming the dynamic pressure groove 38 is approximately 0.6 mm, the cutting resistance A dynamic pressure groove having a depth of about 5 μm can be formed by cutting with a low cutting tool. As a result, the required bearing rigidity can be ensured while reducing the influence on the generated dynamic pressure due to the variation in the depth of the dynamic pressure groove. Therefore, it is possible to suppress the performance degradation of the device equipped with the fluid dynamic pressure bearing. In addition, although it is preferable that the thickness of the cylindrical part of the part which forms a dynamic pressure groove is thin, when the thickness becomes thinner than 0.2 mm, possibility that it will deform | transform by the handling at the time of an assembly becomes high. Therefore, it is desirable to set it as 0.2-0.6 mm. Further, if the depth of the dynamic pressure groove 38 is to be made to exceed approximately 8 μm under the same conditions as the processing method of the present embodiment, it is necessary to reduce the number of rotations during processing, and processing time increases. Further, when the fluid dynamic pressure bearing is caused to function, the amount of the lubricant flowing into the dynamic pressure groove increases and the flow load increases. As a result, an increase in current for rotating the rotary shaft is caused, and therefore the depth of the dynamic pressure groove 38 is preferably in the range of 3 μm to 8 μm.

  The herringbone-shaped dynamic pressure groove 38 as described above is substantially V-shaped. The dynamic pressure groove 38 collects the lubricant along the ridge at the V-shaped linear portion and concentrates the lubricant on the folded portion to generate dynamic pressure. The radius of the folded portion of the dynamic pressure groove formed by conventional ball rolling is about R0.3 mm. FIG. 8A is a schematic diagram showing a case where the dynamic pressure groove 38 is formed by ball rolling and the radius R1 of the folded portion 46 is large. In this case, the straight portion 48 is shortened, the efficiency of scraping the lubricant is poor, and the pressure relief is also increased. As a result, there is a problem that the generated dynamic pressure P1 is also lowered and the resistance in the rotation direction is increased.

  On the other hand, in this embodiment, the bearing base material that becomes the shaft housing portion is formed of, for example, a copper-based material. Then, by using the fluid dynamic pressure bearing manufacturing method described above, the dynamic pressure groove having a depth of about 5 μm is formed by cutting using a cutting tool having an inner diameter of 2 to 4 mm and a tip radius of 0.05 mm. 38 is formed. As a result, as shown in FIG. 8B, the radius R2 of the folded portion 46 of the herringbone-shaped dynamic pressure groove 38 can be reduced to 0.05 mm. As a result, the straight portion 48 becomes longer, and the efficiency of scraping of the lubricant can be increased. For this reason, it becomes possible to reduce the escape of the pressure in the folding | returning part 46, and the generated dynamic pressure P2 can be raised. That is, the rotational load is reduced and the current required for driving the rotating shaft can be reduced. Further, since the bearing portion can be relatively miniaturized, it is possible to contribute to the reduction in the current required for miniaturization and driving of the device including the fluid dynamic pressure bearing. The radius R of the folded portion 46 is preferably small. However, if R is smaller than 0.02 mm, the wear of the cutting tool used for cutting increases, the tool life is shortened, and the cutting pitch becomes fine. The problem is that the time is long. On the contrary, a test result has been obtained that the above-mentioned effect cannot be expected when the radius R of the folded portion 46 is greater than 0.1 mm. Therefore, the radius of curvature R of the folded portion 46 is preferably 0.02 to 0.1 mm.

  By the way, with respect to the herringbone-shaped dynamic pressure groove 38, if the dynamic pressure groove depth at the corner of the folded portion 46 is deep, the inner wall surface of the corner becomes an obstacle to the flow of the lubricant, and the radius of the shaft housing hole 44 is increased. This may hinder efficient dynamic pressure generation in the direction. Further, if dynamic pressure cannot be generated efficiently, it becomes a rotational load of the rotating shaft, which causes an increase in current for rotation. FIG. 9A is an enlarged view of the folded portion 46 of the dynamic pressure groove 38, and the arrow represents the flow of the lubricant. FIG. 9B shows an enlarged view of the folded portion 46 of the dynamic pressure groove 38 when the dynamic pressure groove depth at the corner of the folded portion 46 is the same depth as the straight portion 48. Yes. In the case of such a shape, the processing of the dynamic pressure groove 38 is easy, but the ratio of the lubricant flowing into the dynamic pressure groove 38 being rebounded on the inner wall surface of the corner portion of the folded portion 46 is indicated by an arrow. In some cases, the pressure component increases in a direction that does not contribute to the dynamic pressure for supporting the rotating shaft in the radial direction.

  On the other hand, in the present embodiment, the bearing base material that becomes the shaft housing hole 44 is formed of, for example, a copper-based material. Then, by using the fluid dynamic pressure bearing manufacturing method described above, the cylindrical portion has an inner diameter of 2 to 4 mm, and the dynamic pressure groove 38 is formed by cutting with a cutting force having a low cutting resistance. At this time, the cutting amount of the cutting tool 20 is adjusted by adjusting the amplitude of the piezoelectric element 28 of the first X-axis driving unit 24 so that the dynamic pressure groove depth at the corner of the folded portion 46 is approximately 2 μm. On the other hand, the hydrodynamic groove depth of the other straight part 48 is set to approximately 5 μm so that the folded part 46 and the straight part 48 are connected with a taper as shown in FIG. 9C. Thus, by forming the depth of the dynamic pressure groove at the corner of the folded portion 46 shallower than the other portions, the ratio of the lubricant rebounding on the wall surface inside the corner of the folded portion 46 is lowered. . As a result, the pressure component in the direction contributing to the dynamic pressure for supporting the rotating shaft in the radial direction increases. Thus, by partially reducing the depth of the dynamic pressure groove 38, it is possible to generate sufficient dynamic pressure to improve the rotation accuracy and to increase the bearing rigidity. Further, since the rotational load can be reduced, the current for rotating the rotary shaft can also be reduced. As described above, it is possible to obtain the above-described effect by the fact that the dynamic pressure groove depth at the corner portion of the folded portion 46 is shallower than the dynamic pressure groove depth of other portions, and the depth setting is the above-described numerical value. Not limited to. When cutting the dynamic pressure groove 38 with the cutting tool 20 as in this embodiment, the depth of the dynamic pressure groove 38 can be made constant as shown in FIG. It is also possible to give priority to the performance improvement of the dynamic pressure groove 38 by providing an inclination in the dynamic pressure groove 38 as in 9 (c).

  The bottom surface of the dynamic pressure groove 38 formed by conventional ball rolling is smooth. As a result, the contact angle with respect to the lubricant on the bottom surface is reduced, and the resistance due to the viscosity of the lubricant is increased. In other words, the rotational load increases, causing an increase in current when the rotary shaft is driven to rotate. On the other hand, in the present embodiment, the bearing base material that becomes the shaft housing hole 44 is formed of, for example, a copper-based material. Then, by using the fluid dynamic pressure bearing manufacturing method described above, a herringbone-shaped dynamic pressure groove 38 having a depth of about 5 μm is formed with the cylindrical portion having an inner diameter of 2 to 4 mm. In this embodiment, as shown in FIGS. 5B and 10, a rectifying blade 50 that is elongated in the rotational direction and has a height tw of, for example, 1 μm is provided on the bottom surface of the dynamic pressure groove 38. The rectifying blade 50 is a blade that faces the rotation direction of the rotating shaft, and does not cause a resistance to the rotation direction. On the other hand, for the lubricant flowing along the shape of the dynamic pressure groove 38, the contact angle increases due to the presence of the rectifying blade 50, and the substantial viscosity of the lubricant at the bottom surface of the dynamic pressure groove 38 may be reduced. it can. As a result, the current can be reduced by reducing the rotational load. The straightening blade 50 may be cut out exclusively. However, the straightening groove 40 is formed in the process of continuously forming the linear groove 40 in the Z-axis direction by adjusting the tip radius of the cutting tool 20 and the feed pitch. Eyes (blade marks) may be substituted. Further, as described above, the linear groove 40 can be formed by adjusting the amplitude of alternating drive of the piezoelectric element 28 even if the inner peripheral surface of the workpiece 16 is tapered as shown in FIG. The rectifying blade 50 can be formed in the process of continuously forming the linear groove 40 in the Z-axis direction, and the rectifying blade 50 can be easily formed even on the workpiece 16 having a tapered inner peripheral surface. As a result, a high-performance fluid dynamic pressure bearing with low rotational resistance can be easily produced.

  FIG. 11 is a cross-sectional view of a main part of a disk drive device 52 that drives a hard disk to which the fluid dynamic pressure bearing of this embodiment is applied. In FIG. 11, for convenience, the side indicated by the arrow A is the upper side (upper), and the side indicated by the arrow B is the lower side (lower). The disk drive device 52 includes a fixed body, a radial fluid dynamic pressure bearing, a thrust fluid dynamic pressure bearing, and a rotating body. The number of rotations of the rotating body is, for example, 5400 times / minute.

  The fixed body includes a base member 54, a stator core 56 fixed to the outer peripheral surface of the cylindrical portion 54a provided on the base member 54, an annular housing member 58 fixed to the inner peripheral surface of the cylindrical portion 54a, and a housing. And an annular shaft housing member 60 having a cylindrical portion inner periphery 60a fixed to the inner peripheral surface of the member 58.

  The stator core 56 has a coil 62 wound around a plurality of salient poles protruding outward. The shaft housing member 60 has a shape in which a cylindrical portion 60b that houses the rotating shaft 66 and a flange portion 60c that extends outward on one end side of the cylindrical portion 60b are coupled. The housing member 58 includes a cylindrical portion that fits the shaft housing member 60 into the inner periphery, a bottom portion that seals one end portion of the cylindrical portion, and an upper end surface portion that is provided at the other end and has an axial surface. Cup-shaped parts.

  The rotating body includes a cup-shaped hub 64, a rotating shaft 66 fixed to the center hole 64 a of the hub 64, a ring-shaped magnet 68, and a thrust member 70. The hub 64 includes a first cylindrical portion 64c that is concentric with the center hole 64a and has a small diameter, a second cylindrical portion 64b that is disposed outside, and a hub extension portion 64d that extends outward from the end of the second cylindrical portion 64b. It is configured. A thrust member 70 is fixed to the inner peripheral surface of the first cylindrical portion 64c, and a ring-shaped magnet 68 is fixed to the inner peripheral surface of the second cylindrical portion 64b.

  A step portion 66 a is provided on the connection side of the rotation shaft 66 to the hub 64, and the rotation shaft 66 is press-fitted into the center hole 64 a of the hub 64 so that both are integrated. The thrust member 70 has a shape in which a thin disk portion in the axial direction having a thrust upper surface 70a and a thrust lower surface 70b and a drooping portion 70d long in the axial direction are coupled to the lower surface on the outer peripheral side. The inner peripheral surface of the hanging part 70d has a tapered shape with a radius that decreases toward the tip, and the lubricant filled in the gap of the fluid dynamic pressure bearing by capillary action in cooperation with the outer peripheral surface of the housing member 58 is externally applied. The capillary seal part which prevents leaking out is configured.

  The disc portion of the thrust member 70 is disposed through a narrow gap between the lower surface of the flange portion 60 c of the shaft housing member 60 and the upper end surface of the housing member 58, and the outer periphery of the hanging portion 70 d is the first cylindrical portion of the hub 64. A thrust fluid dynamic pressure bearing is configured by fixing thrust dynamic pressure grooves on both surfaces of the thrust upper surface 70a and the thrust lower surface 70b.

  The radial fluid dynamic pressure bearing is composed of a rotary shaft 66 and a shaft storage member 60 that stores the rotary shaft 66 and rotatably supports it. The shaft housing member 60 includes a herringbone-shaped first radial dynamic pressure groove and a second radial dynamic pressure groove (not shown) disposed on the inner peripheral surface thereof in an axial direction, and the first radial dynamic pressure. It has a circumferential recess 60d disposed in the middle of the groove and the second radial dynamic pressure groove. The gap between the outer peripheral surface of the rotating shaft 66 and the inner peripheral surface of the shaft housing member 60 is filled with a lubricant.

  In this embodiment, the shaft housing member 60 is formed of a copper-based material. By using the fluid dynamic pressure bearing manufacturing method described above, the inner diameter of the cylindrical portion is 2.5 mm, and the thickness of the portion where the dynamic pressure groove 38 is formed is approximately 0.6 mm. Then, the dynamic pressure groove 38 having a depth of about 5 μm is formed by cutting using a cutting tool having a tip radius R of about 0.05 mm. The radius R of the folded portion 46 of the herringbone-shaped dynamic pressure groove 38 is 0.05 mm. The rotating body is rotatably supported by the radial fluid dynamic pressure bearing and the thrust fluid dynamic pressure bearing, and is driven to rotate by the electromagnetic action of the stator core 56 and the magnet 68. A magnetic disk (not shown) is mounted on the outer periphery of the hub 64, and data recording / reading is executed by a read / write unit (not shown).

  By mounting the fluid dynamic pressure bearing of this embodiment on the disk drive device 52 configured in this way, the disk drive device 52 capable of high precision, small size, light weight, and low current can be efficiently and at low cost. Can be created. In the present embodiment, the method of machining the groove inside the shaft housing member 60 constituting the radial fluid dynamic pressure bearing has been described. In another embodiment, the processing method of this embodiment may be applied when a dynamic pressure groove is formed on the rotating shaft 66 side. Further, the present invention may be applied when a dynamic pressure groove is formed in a member constituting the thrust fluid dynamic pressure bearing. And in any case, the dynamic pressure groove which can contribute to small size and light weight with high precision can be created efficiently. Further, by using the rotary shaft and the thrust fluid dynamic pressure bearing formed as described above, the performance of the disk drive device can be improved.

  The present invention is not limited to the above-described embodiment, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The configuration shown in each figure is for explaining an example, and any configuration that can achieve the same function can be changed as appropriate, and the same effect can be obtained.

It is explanatory drawing of the manufacturing apparatus used for the fluid dynamic pressure bearing manufacturing method of a present Example. In FIG. 1, it is an upper view explaining centering on a workpiece | work and a byte mounting part. It is explanatory drawing explaining the sinusoidal drive voltage waveform used when driving the piezoelectric element of a present Example. It is explanatory drawing which shows typically the relationship between the workpiece | work and a byte in the manufacturing method of a present Example. (A) is a schematic diagram showing a process of forming a herringbone-shaped dynamic pressure groove in the present embodiment developed on a plane, and (b) is a diagram showing a dynamic pressure groove formed by continuous linear grooves. It is explanatory drawing explaining the state which comprises. It is explanatory drawing explaining processing to the taper-shaped shaft accommodation hole part, changing the amplitude of the alternating drive of a piezoelectric element corresponding to a taper shape. It is explanatory drawing explaining that two sets of herringbone-shaped dynamic pressure grooves are formed in the axial direction with an intermediate portion sandwiched between shaft housing holes. (A) is a dynamic pressure groove formed by ball rolling, and is a schematic diagram showing a case where the radius of the folded portion is large, (b) is a dynamic pressure groove formed by the processing method of the present embodiment, It is a schematic diagram which shows the case where the radius of a folding | returning part is small. (A) is an enlarged view of the folded portion of the dynamic pressure groove, (b) is an enlarged sectional view showing the folded portion of the dynamic pressure groove when the groove depth is constant, (c) this embodiment It is an expanded sectional view which shows the folding | turning part of the dynamic pressure groove formed by the manufacturing method of. It is explanatory drawing explaining the baffle blade formed in a dynamic pressure groove. It is principal part sectional drawing of the disk drive device which drives the hard disk to which the fluid dynamic pressure bearing of a present Example is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus, 12 Base, 14 Rotation drive part, 16 Workpiece, 18 Chuck, 20 byte, 22 byte mounting part, 24 1st X-axis drive part, 26 2nd X-axis drive part, 28 Piezoelectric element, 30 Displacement sensor, 32 Pulse transmitter, 34 Piezoelectric element drive power supply, 36 Displacement sensor controller, 38 Dynamic pressure groove, 40 Linear groove, 42 Intermediate part, 44 Shaft receiving hole part, 46 Folding part, 48 Linear part, 50 Rectifier blade, 52 Disk drive device.

Claims (8)

By supporting a bearing base material having a shaft housing hole at the center and rotating the bearing base material around its central axis, the inner surface of the shaft housing hole is cut by a cutting tool to form a dynamic pressure groove. A method of manufacturing a fluid dynamic pressure bearing comprising:
The circumferential width of the dynamic pressure groove formed on the inner peripheral surface of the shaft housing hole by the cutting tool that is micro-alternatively driven in a second processing direction perpendicular to the first processing direction along the central axis of the bearing base material. A linear groove forming step of forming a linear groove having a corresponding length along a circumferential direction of a surface orthogonal to the first processing direction;
The relative position of the bearing base material and the cutting tool is displaced in the first machining direction, the linear groove is continuously formed in the first machining direction, and the dynamic pressure groove extending in the first machining direction is extended. Extending process;
Including
The shaft housing hole portion has a tapered shape in which both end sides of the bearing base material are smaller in diameter than the inner side, and the cutting tool is alternated in the second machining direction according to the displacement amount and the taper angle in the first machining direction. A method of manufacturing a fluid dynamic pressure bearing, comprising adjusting a depth of a dynamic pressure groove extending by changing an amplitude amount during driving. The manufacturing method of the fluid dynamic bearing according to claim 1, wherein a radius of a tip of the cutting tool is 0.02 mm to 0.1 mm. A fluid dynamic pressure bearing manufactured using the fluid dynamic pressure bearing manufacturing method according to claim 1 . The fluid dynamic pressure bearing according to claim 3 , wherein an inner diameter of the inner peripheral surface of the shaft housing hole is 2 mm to 4 mm. 5. The fluid dynamic pressure bearing according to claim 3 , wherein a thickness of a portion of the bearing base material where the dynamic pressure groove is formed in the shaft housing hole is 0.2 mm to 0.6 mm. . The dynamic pressure groove includes a first radial dynamic pressure groove and a second radial dynamic pressure groove that are spaced apart in the axial direction on the inner peripheral surface of the shaft housing hole portion,
Said first radial dynamic pressure groove and the second radial dynamic pressure groove is herringbone pattern, according to claim 3 in which dynamic pressure grooves depth of the bent portion is equal to or shallower than the dynamic pressure groove depth of the other portion fluid dynamic bearing according to any one of claims 5 to. The fluid dynamic pressure bearing according to any one of claims 3 to 6 , wherein a rectifying blade is formed on a bottom surface of the dynamic pressure groove along a circumferential direction of the shaft housing hole portion. . Disk drive apparatus comprising the fluid dynamic bearing according to any one of claims 7 claims 3.

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