JP2005180467A - Dynamic pressure fluid bearing motor with variable opening - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a dynamic pressure fluid bearing motor enabling the precise control of floated amount without a thrust bearing larger in size than its shaft diameter. <P>SOLUTION: The precise floated amount control in association with a spiral groove equal in size to approximately the small shaft diameter is enabled by generating the most of a load capacity for supporting a rotating part by force-feeding a lubricating fluid to near the end of the shaft by the unbalance herringbone groove of a radial bearing. A circulating passage opening is formed in a sleeve end part which can be easily performed by precise machining or a counter plate to form the variable opening in association with a flat shaft end. Since the flow velocity of the lubricating fluid can be set to the minimum, the possibility of leakage of the lubricating fluid can be reduced, shaft damage can be reduced, and a thin, low power consumption magnetic disk using the dynamic pressure fluid bearing motor can be provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrodynamic bearing motor, and more particularly to a hydrodynamic bearing motor suitable for a high-speed rotation and thin magnetic disk drive (HDD).

  Since conventional hydrodynamic bearings for HDDs need to strictly control the axial position while maintaining the attitude of the rotating part, the rotating part is configured with a radial bearing, and the axial position is shared with a thrust bearing. In addition, it had a thrust bearing part larger in diameter than the shaft.

  With the trend toward miniaturization of HDDs, hydrodynamic bearing motors are also becoming smaller and thinner. In order to ensure radial bearing span, the present inventors have gradually developed a single thrust structure in which the thrust bearing previously invented is formed on the rear surface of the hub. Has become dominant. This contributes to reducing the axial loss by reducing the area where the lubricating fluid flows and friction, and further improving the assembly.

  However, the presence of a thrust bearing or thrust plate larger than the remaining shaft diameter has a region where the lubricating fluid flows at high speed only for the purpose of regulating the axial position of the rotating part. It always left a threat of leakage and a difficulty in reducing axial loss.

  The above problems can be improved by realizing a hydrodynamic bearing that precisely supports the rotating part with only a shaft and a sleeve without a thrust bearing or thrust plate, but such a configuration is dominated by today's bearing configuration. Various developments were attempted before becoming. They consist of a structure that always slides in contact with the center of the shaft end, a structure that floats with a small spiral groove at the shaft end, a structure that floats and supports the rotating part by magnetic repulsion or magnetic attraction, and lubricating fluid for radial bearings. For example, the load capacity in the axial direction is obtained by pumping.

  The first configuration that slides and rotates the shaft end has become quite realistic today when the weight of the rotating part has decreased, but it still has a point in which axial damping is difficult to work against and impact has been added. Considering the influence of the indentation due to, it is not suitable for use in HDD.

  The second configuration having a small spiral groove at the shaft end is proposed in, for example, Japanese Examined Patent Publication No. 46-8046. However, in the case of a small shaft diameter, a sufficient load capacity cannot be obtained at low speed rotation, so the flying height is small. It has a weak point that the sliding distance at the start and stop of rotation becomes large.

  The third configuration that supports the rotating part using the magnetic repulsive force or attractive force cannot achieve the positional accuracy in the axial direction, and has problems such as an increase in the number of parts, which is practical for small HDD applications. Not.

  In a fourth configuration using the lubricating fluid pumping capability of the radial bearing, the lubricating fluid is pumped into a gap formed by the bottom of the bottomed sleeve and the shaft end to obtain an axial load capacity. The lubrication fluid pumping of radial bearings is efficient and powerful enough to support the rotating body, but there are difficulties in precise control of flying height. There are two types of realistic proposals. One is a structure that controls the flying height by forming a variable opening along with the position of the shaft end that has a circulation path opening on the sleeve peripheral wall, and the shaft end and sleeve It is the structure which controls the flying height by forming an orifice between them.

  The former of the fourth configuration is proposed in Japanese Patent Publication No. 48-4498, and is formed by a shaft and a circulation path opening provided in the peripheral wall of the sleeve. It is difficult to ensure the accuracy of the above, and it is difficult to obtain a uniform flying height on the order of several micrometers as a HDD bearing.

  The latter configuration of the fourth configuration is proposed in Japanese Patent Laid-Open Nos. 58-24615, 58-24616, 58-54223, etc. to improve the flying height accuracy. It is difficult to control the flying height larger than the directional gap. In the current hydrodynamic bearing motor for HDD, the radial clearance is about 2 microns, and the flying height in the axial direction is about 5 microns, so it is difficult to apply to products because it wants to secure a margin for shock and vibration.

  For the reasons described above, any of the above-described methods proposed heretofore is difficult to adopt in current HDDs. However, since the radial bearing has a narrow radial gap, it is efficient and powerful, so there is a possibility of realizing high-precision control of the flying height of the rotating part by improving the fourth configuration.

Japanese Patent Publication No.46-8046 "Fluid sliding bearing device"

Japanese Patent Publication No. 48-4498 "Hydrodynamic sliding bearings for axial and axial loads" Japanese Patent Application Laid-Open No. 58-24615 “Hydrodynamic Fluid Bearing Device” Japanese Patent Laid-Open No. 58-24616 "Hydrodynamic Fluid Bearing Device" Japanese Patent Laid-Open No. 58-54223 “Dynamic Pressure Spindle Device”

  Accordingly, an object of the present invention is to provide a dynamic pressure that enables high-speed rotation, thinning, low shaft loss, low cost, etc. by precisely controlling the flying height of the rotating part without having a thrust bearing larger than the shaft diameter. It is to realize a fluid dynamic bearing motor and to realize a thin and low power consumption magnetic disk device.

  The basic concept of the hydrodynamic bearing motor according to the present invention consists of a cylindrical shaft and a bottomed sleeve that are relatively rotatably fitted, a lubricating fluid in the gap between the shaft and the sleeve, and a magnetic field between the rotating portion and the fixed portion. In a hydrodynamic bearing motor configured with magnetic means for generating an attractive force, the shaft surface or the inner peripheral surface of the sleeve has an unbalanced herringbone groove having a pumping ability in the sleeve bottom direction and the shaft There is a circulation path in the shaft or in the sleeve that connects the vicinity of the end and the side far from the shaft end of the unbalanced herringbone groove. The first axial load capacity generating means by the orifice is provided in the circulation path, and the second axial load capacity generating means depending on the flying height is provided in the vicinity of the shaft end, and the unbalanced herringbone groove has the rotating portion attitude. A radial bearing dynamic pressure is generated for holding, and a lubricating fluid is pumped to the bottom surface side of the sleeve to balance the first and second axial load capacities with the magnetic attraction force and the weight of the rotating part, thereby to It is characterized by controlling the flying height.

  The bottomed sleeve is constituted by a cylindrical sleeve and a counter plate fixed to the end face, and a part of the circulation path is constituted by a recessed channel formed between the sleeve end face and the counter plate. A variable opening that changes in accordance with the flying height of the rotating part is configured by the circulation path opening that is a cross section of the recessed channel and the outer peripheral part of the shaft end, and serves as the first and second axial load capacity generating means. Implement precise control. Since the recessed channel on the sleeve end face or counter plate surface can be formed by using various micromachining techniques, the opening cross section and position are highly accurate, and the defect that the flying height cannot be precisely controlled with the conventional structure can be overcome.

  Furthermore, a pump-in spiral groove is formed at the shaft end or sleeve bottom, and the flying height is controlled in combination with a substantially variable opening to increase the axial support rigidity and enable precise flying height control. In that case, if the parameter is set so that the maximum axial load capacity due to only the variable aperture is approximately equal to the sum of the magnetic attractive force and the weight of the rotating part, the load capacity due to the spiral groove due to low speed rotation or small shaft diameter, etc. Rotation of the rotating part can be ensured even when is small.

  When the access hole for the lubricating fluid that is connected to the circulation path in the sleeve and communicated with the atmosphere at the sleeve end face is gradually increased so that the lubricating fluid forms an interface with the air, the access hole on the sleeve end face This makes it easy to monitor the interface level of the lubricating fluid and inject the lubricating fluid. Further, when bubbles are mixed in the lubricating fluid, the bubbles are stochastically released from the interface with the atmosphere in the access hole in the process of circulating the lubricating fluid and bubbles in the circulation path, and the lubricating fluid is The bubbles inside can be removed.

  A radial bearing is used as an unbalanced herringbone groove, and a lubricating fluid is pumped to the shaft end portion to generate most of the load capacity of the rotating portion support. The gap in the radial direction is small and easy to manage, so it is energy efficient, powerful, and capable of precise flying height control in cooperation with a spiral groove with a small shaft diameter.

  In the present invention, a circulation path opening is provided in the sleeve end portion or the counter plate, which is easy to perform precision processing, and a substantial variable opening is formed together with the movement of the shaft end.

  In addition, the structure with an access hole that has an interface with the atmosphere continuously in the circulation path in the sleeve makes it easy to inject oil and control the level under atmospheric pressure, simplifying the assembly process of the bearing and further reducing the cost. To.

  By using the above-mentioned hydrodynamic bearing motor, it is possible to realize a magnetic disk device having the characteristics of thinning, high track density recording by small shaft touch, and low power consumption by low axial loss.

  The hydrodynamic bearing motor according to the present invention will be described below with reference to the drawings, with respect to embodiments, principles, and actions. However, before describing the embodiments of the present invention, the novelty of the present invention can be easily understood. An example of a conventional structure will be described with reference to FIGS.

  FIG. 10 shows a structure proposed in Japanese Patent Publication No. 48-4498, in which a lubricating fluid is pumped by a radial bearing to lift the rotating portion in the axial direction to control the position. In this figure, a cylindrical shaft 101 is opposed to the sleeve 102 with a minute gap, and its tip 104 is conical and in contact with the bottom surface of the sleeve 102 when stationary. On the surface of the cylindrical shaft 101, a spiral groove 103 for pumping the lubricating fluid toward the bottom surface of the sleeve 102 during rotation is arranged, and a circulation path 106 having an opening 107 is formed on the inner peripheral surface of the sleeve 102. The cylindrical shaft 101 is opposed to the opening 107 with a minute gap to form a substantially variable opening.

  When the cylindrical shaft 101 rotates, the spiral groove 103 pumps the lubricating fluid toward the bottom surface of the sleeve 102 to increase the pressure of the lubricating fluid in the pressure chamber 105, so that the cylindrical shaft 101 is pushed up, and the lubricating fluid inflow area of the opening 107 is large. Thus, the lubricating fluid flowing into the circulation path 106 increases and the lubricating fluid pressure in the pressure chamber 105 decreases, so that the flying height is stabilized at a position where the weight of the rotating part including the cylindrical shaft 101 is supported.

  In general, radial bearings are easy to manage in the radial direction and are efficient and strong, so that they can cope with a considerably large rotating part weight. However, in the conventional example of FIG. 10, it is difficult to precisely control the boundary between the cylindrical shaft 101 facing the opening 107 and its tip end 104 and the angle of the conical tapered surface, and the bottom surface of the sleeve 102 of the opening 107. The drawbacks such as difficulty in obtaining the position accuracy from the above are as pointed out in Japanese Patent Laid-Open No. 58-24615, and precise control of the flying height of the rotating part is not possible. In today's HDDs, it is required to control the flying height of the rotating part within the range of 5 to 10 microns, but it is difficult to adapt.

  FIG. 11 shows an example of the structure of Japanese Patent Laid-Open No. 58-24616, which is an improvement of Japanese Patent Publication No. 48-4498. In the figure, a cylindrical shaft 111 has a spiral groove similar to that shown in FIG. 10 on the outer peripheral surface, and is opposed to the sleeve 112 at a minute gap and is opposed to the ball 113 fixed to the sleeve 112 at the shaft end. A circulation path 114 is provided in the cylindrical shaft 111, and the opening 115 is provided at the shaft end of the cylindrical shaft 111.

  When stationary, the shaft end of the cylindrical shaft 111 comes into contact with the ball 113 and substantially closes the opening 115. When the cylindrical shaft 111 rotates, a spiral groove (not shown) pumps the lubricating fluid in the axial direction, and the opening 115 is pushed by the ball 113. Since it is blocked, the pressure of the lubricating fluid in the pressure chamber 116 is increased, and the rotating part including the cylindrical shaft 111 is floated in the axial direction. When the shaft end of the cylindrical shaft 111 moves away from the ball 113, the amount of lubricating fluid flowing into the opening 115 increases and the lubricating fluid pressure in the pressure chamber 116 decreases, so that the cylindrical shaft 111 floats at an appropriate position for supporting the weight of the rotating part. To do.

  Although a variable opening is formed between the shaft end and the ball 113 by the flying height of the cylindrical shaft 111, the controllable flying height is limited to a value similar to the radial clearance between the cylindrical shaft 111 and the sleeve 112. It is done. With the hydrodynamic bearing motor of HDD, the radial clearance is set to about 2 microns, and the axial flying height is about 5 to 10 microns at room temperature considering the expected impact force and operating temperature range. I want to set it, but it's not the right way.

  As described above with reference to FIGS. 10 and 11, the conventionally known method of controlling the floating position of the rotating portion with the radial bearing has insufficient flying height position accuracy, or the controllable flying height range is not appropriate. Therefore, it cannot be applied to the HDD as it is. The present invention improves the drawbacks of these conventional structures and realizes a hydrodynamic bearing that can be applied to an HDD even with a simple bearing configuration including only a shaft and a sleeve.

  FIG. 1 shows a longitudinal section and a view of a sleeve end face of an HDD hydrodynamic bearing motor according to a first embodiment of the present invention. In the figure, a hydrodynamic bearing is mainly composed of a shaft 11, a sleeve 12, a counter plate 13, a lubricating fluid filled in a gap, and the shaft 11 is connected to a hub 14 having a disk mounting surface and further to the hub 14. The rotor magnet 16 is fixed to form a rotating portion, and the sleeve 12 includes a base plate 15, and the base plate 15 includes a rotating driving stator core 17, a coil 18, and the like to form a fixed portion. Reference numeral 19 denotes a magnetic piece that is fixed to the base plate 15 so as to face the rotor magnet 16 and generates a magnetic attractive force that attracts the rotating portion in the axial direction. Reference numeral 1k is a retainer for restricting the axial displacement of the rotating part.

  The sleeve 12 has unbalanced herringbone grooves 1a and 1b on the inner peripheral surface facing the shaft 11, and has circulation holes 1d and 1f and an access hole 1h. The end face of the shaft 11 has a pump-in spiral groove 1c. The circulation holes 1d and 1f are small holes having a diameter of about 0.4 millimeters, and the access hole 1h opens to the upper end surface of the sleeve 12 with the diameter gradually increasing continuously with the circulation hole 1d. The circulation hole 1f is a small hole that communicates between the unbalanced herringbone grooves 1a and 1b, and forms a circulation path for the lubricating fluid with the recessed channel 1e and the circulation hole 1d that communicate with the shaft end.

  The recessed channel 1e is precisely formed on the sleeve end face by an etching technique. The dimensions vary depending on the size of the bearing and the weight of the rotating part, but the width is several tens to several hundreds of micrometers and the depth is about 40 micrometers at most. In addition, electric discharge machining, electrolytic machining, ion milling, precision cutting, etc. can be used.

  The shaft 11 and the sleeve 12 are opposed to each other with a minute gap of about 2 microns, and the gap has a lubricating fluid, but the shaft 11 is reduced in diameter so that the gap becomes large at the upper end of the minute gap. Part 1j. The lubricating fluid is substantially sealed at the seal portion 1j and the access hole 1h with an interface with air due to surface tension. Reference numeral 1g indicates an interface of the lubricating fluid in the access hole 1h.

  The herringbone groove is composed of a combination of two spiral grooves that pump the lubricating fluid in the opposite direction as it rotates, but the unbalanced herringbone groove 1a, 1b is constructed by shortening the length of the spiral groove on the bottom side of the sleeve 12. , The lubricating fluid is pumped toward the bottom of the sleeve 12 during rotation. The shape of the unbalanced herringbone grooves 1a and 1b provided on the sleeve 12 will be described with reference to FIG. FIG. 3 shows a perspective view of the sleeve 12 divided vertically, and shows upper and lower herringbone grooves 1a and 1b formed on the inner peripheral surface. The shape and size of the dynamic pressure generating groove varies depending on the gap, the viscosity of the lubricating fluid, the target performance, etc., but the upper and lower herringbone grooves 1a and 1b are usually formed to a depth of about 6 microns. The lower herringbone groove 1b is composed of spiral grooves having axial lengths L1 and L2, and L1 is set to be larger than L2 as shown in FIG. Number 31 indicates the direction of rotation of the shaft 11. Reference numeral 1 f indicates an outlet of a circulation hole provided in the sleeve 12.

  The magnetic piece 19 is made of a magnetic material such as a silicon steel plate, ferrite, or permalloy, and generates a magnetic attractive force between the rotating portion and the fixed portion in cooperation with the rotor magnet 16. It is set to about 3 to 5 times the weight of the rotating part including the magnetic disk, hub 14, rotor magnet 16, shaft 11 and the like. When the magnetic attractive force is insufficient only by the magnetic piece 19, the positions of the stator core 17 and the rotor magnet 16 are displaced in the axial direction to generate the magnetic attractive force, or the counter plate 13 is magnetized by embedding a magnet at the tip of the shaft 11. Supplement the magnetic attraction as a body.

  FIG. 2 is a perspective view illustrating the end face of the sleeve 12 and the end portion of the shaft 11 for supplementary explanation of FIG. In this figure, a recessed channel 1e formed on the end surface of the sleeve 12 has a substantially rectangular opening 21 on the inner peripheral surface of the sleeve 12, and the end surface of the shaft 11 pumps the lubricating fluid in the axial direction along with rotation. In spiral groove 1c. In FIG. 2, the shaft 11 is shown behind the normal use for easy viewing.

  The center of the shaft end is a point indicated by reference numeral 22, but the center of the spiral groove 1c is slightly shifted from the shaft end center 22 as indicated by reference numeral 23. This is a structure that takes into account that if the pressure distribution of the lubricating fluid formed by the spiral groove 1c is axisymmetric, bubbles are likely to stay at the center of the axis.

  Further, the shaft end slides in contact with the counter plate 13 at the time of starting and stopping the rotation, but in order to avoid damage, the surface of the counter plate 13 is coated with a solid lubricant mainly composed of molybdenum disulfide of about 10 microns. Even if DLC is formed to a few micrometers in addition to diverted molybdenum, sliding resistance is reduced and it is effective for wear prevention.

  The outer peripheral portion of the shaft 11 only has a gap of about 2 microns with the inner peripheral surface of the sleeve 12, and the end surface of the shaft 11 is formed so as to be orthogonal to the shaft 11 at least in the vicinity of the outer periphery. The variable opening is formed by changing the opening area of the opening 21 as the shaft 11 floats. Since the opening 21 is formed as a cross section of the recessed channel 1e on the end face of the sleeve 12, the position and shape can be easily controlled. The lubricating fluid circulates through the unbalanced herringbone groove 1b, the recessed channel 1e, and the circulation holes 1d and 1f. When the recessed channel 1e is closed by the shaft 11, the substantial inflow area of the lubricating fluid is substantially the same as that of the shaft 11. Naturally, it should be set to be smaller than the product of the gap length formed by the sleeve 12 and the outer peripheral length of the shaft 11. In the opposite case, the flow resistance before the variable opening becomes large, and the effect of the variable opening is diminished.

  The variable opening 21 formed by the shaft 11 and the opening 21 generates a first axial load capacity that decreases with the flying height, and the spiral groove 1c at the shaft end generates a second axial load capacity that decreases with the flying height. In the first embodiment of the present invention, the maximum value of the first axial load capacity is set to be equal to or greater than the value obtained by adding the rotating portion weight to the magnetic attractive force. The purpose and operating principle will be described with reference to FIG.

  When stationary, the shaft 11 is in contact with the counter plate 13 mainly by magnetic attraction. As the rotation starts, the spiral groove 1c pumps the lubricating fluid between the shaft end and the counter plate 13 in the axial direction to generate a second axial load capacity. At the same time, the unbalanced herringbone groove 1b moves the lubricating fluid in the axial direction. To generate a first axial load capacity. The lubricating fluid pumped by the unbalanced herringbone groove 1b circulates to the side farther from the shaft end of the unbalanced herringbone groove 1b through a circulation path formed by the recessed channel 1e, the circulation holes 1d, 1f and the like. On the other hand, the unbalanced herringbone groove 1a also pumps the lubricating fluid in the axial direction and supplies it to the unbalanced herringbone groove 1b to help quick ascent at start-up. The lubricating fluid interface is moved to the extent that it is eliminated.

  FIG. 4 illustrates the operating principle in which the position of the rotating unit is controlled with the flying height FH on the horizontal axis and the axial load capacity LC on the vertical axis. In the figure, reference numeral 41 denotes a first axial load capacity generated by the unbalanced herringbone groove 1b and the variable aperture. It shows the maximum value when the flying height is zero, and gradually decreases as the flying height increases. Reference numeral 42 denotes a second axial load capacity by the spiral groove 1c at the shaft end, and reference numeral 43 denotes a sum of the first and second axial load capacity.

  The HDD is used in the upright position shown in FIG. 1 or upside down, or in the horizontal position, and in mobile applications, vibration may be further applied. This is a point that differs greatly from the usage conditions of polygon scanners, VCRs, and the like, and it is a point that must be considered with respect to design specifications. The force applied between the rotating part and the fixed part varies depending on the posture. If it is upright as shown in FIG. 1, the value obtained by adding the weight of the rotating part to the magnetic attraction force is reversed. The value obtained by subtracting the rotating part weight from the force corresponds.

  Reference numeral 44 indicates a value obtained by adding the rotating portion weight to the magnetic attractive force, and reference numeral 45 indicates a value obtained by subtracting the rotating portion weight from the magnetic attractive force. Accordingly, the flying height f1 at the position where the number 44 and the number 43 intersect in the upright state, and the flying height f2 at the position where the number 45 and the number 43 intersect in the inverted position.

  In the first embodiment of the present invention, the maximum value of the first axial load capacity is set to be equal to or larger than the value obtained by adding the weight of the rotating part to the magnetic attraction force. The maximum value of the first axial load capacity is the value indicated by the dotted line 41 when FH becomes zero. Therefore, even when the diameter of the shaft 11 is small and the second axial load capacity cannot be sufficiently increased, the floating portion can be reliably lifted. Of course, even when the spiral groove 1c is not provided, the flying height can be precisely controlled according to the gist of the present invention. However, as is apparent from FIG. 4, the second axial direction by the spiral groove 1c is used for the purpose of increasing the rigidity value (LC / FH) as much as possible in order to reduce the flying height fluctuation due to external conditions such as vibration and shock. A configuration that contributes load capacity is desirable.

  In this embodiment, the access hole 1h is continuous with the circulation hole 1d and has a structure having an interface of the lubricating fluid. The unbalanced herringbone groove 1a pumps the lubricating fluid in the axial direction during rotation and accommodates the lubricating fluid in the shaft end portion whose volume has increased with the rotation and floating, and accordingly, the unbalanced herringbone groove 1a. The interface of the lubricating fluid is moved to a position where the imbalance is eliminated. In this case, the lubricating fluid that has caused excess or deficiency at the shaft end is adjusted by the lubricating fluid in the access hole 1h. Although the access hole 1h is not essential, it has an important role in adjusting the lubricating fluid, and has a role of facilitating manufacture by reducing the dimensional tolerance of each part.

  During the rotation, the unbalanced herringbone groove 1b always circulates the lubricating fluid through the circulation path, and the circulation path is connected to the access hole 1h and opened to the atmosphere. In the process of circulating through the circulation path, the bubbles probabilistically escape to the atmosphere from the access hole 1h, and the bubbles are excluded from the lubricating fluid. Therefore, the lubrication fluid injection in the assembly process can be performed under atmospheric pressure, and the interface 1g of the lubrication fluid can be monitored or additional lubrication fluid can be injected from the access hole 1h after the assembly.

  If a small hole for observation is provided in the hub 14 corresponding to the access hole 1h, the lubricating fluid can be monitored at any time after the completion, and if the access hole 1h is modified to be provided on the bottom side opposite to FIG. The lubricating fluid can be monitored from the outside of the HDD.

  Special attention should be paid to the minimum gap in the access hole 1h and the circulation paths 1d and 1f. The interface of the lubricating fluid with the atmosphere has the same curvature at rest with the seal portion 1j and the access hole 1h and reaches equilibrium. Therefore, if the minimum gap in the access hole 1h is too large, the lubricating fluid is liable to leak. A gap adjusting member can be arranged in the access hole 1h to adjust the minimum gap, but the third embodiment facilitates this point.

  The sealing portion 1j and the access hole 1h effectively seal the lubricating fluid by surface tension, but an oil repellent agent is applied to the surfaces constituting the sealing portion 1j and the access hole 1h to stop the smear due to the migration of the lubricating fluid. . In the retaining portion 1k, sliding friction between the rotating portion and the fixed portion does not normally occur, but there is a possibility of contact when an excessive vibration shock is applied. In this case, it is not preferable that abrasion powder is generated. As a countermeasure, it is desirable that one member is formed of a hard member or a solid lubricant such as DLC or molybdenum disulfide is applied.

  FIG. 5 is a view for explaining a second embodiment of the present invention. The configuration of the hydrodynamic bearing motor as a whole is the same as that of the first embodiment shown in FIGS. 1, 2 and 3, and the relationship between the magnetic attractive force, the rotating portion weight, and the first axial load capacity is changed. In the second embodiment. That is, the maximum value of the first axial load capacity is set between [the value obtained by subtracting the rotating part weight from the magnetic attractive force] and [the value obtained by adding the rotating part weight to the magnetic attractive force] in the second embodiment. Take an example. There is a feature that enables precise control of the flying height by making the maximum support rigidity in the axial direction by the spiral groove 1c.

  The meanings of the numbers 41, 42, 43, 44, and 45 in FIGS. 4 and 5 are exactly the same, but their setting conditions are different. Number 41 indicates the first axial load capacity, and the maximum value (value when FH is zero) is set between number 44 and number 45. Therefore, in the upright position, the flying height f3 at a position where the number 44 and the number 43 intersect in FIG. 5 is obtained, and in the inverted position, the flying height f4 is a position at which the number 45 and the number 43 intersect. Compared to the first embodiment, the proximity reaction force by the spiral groove 1c increases the specific gravity and increases the rigidity value (LC / FH), but is suitable for conditions where the shaft 11 has a large diameter or a high rotational speed. Yes.

  FIG. 6 is a view for explaining a third embodiment of the present invention, and shows a longitudinal sectional view of a hydrodynamic bearing motor and a plan view of an end face of a sleeve. The third embodiment has the same operating principle as the first embodiment, but mainly differs in the sleeve structure. FIG. 6 shows only parts different from those in FIG.

  In FIG. 6, the sleeve has a double structure of an inner cylinder 61 and an outer cylinder 62, and a part of the outer peripheral surface of the inner cylinder 61 is flattened to create a crescent-shaped gap between the inner cylinder 61 and the outer cylinder 62. These are formed to have the functions of the circulation path 1d and the access hole 1h in FIG. In other words, the cross section of the gap is a crescent shape, with narrow gap portions 64 at both ends, and a wide gap portion 65 of about 0.3 millimeters or more at the center. When one end of the gap is in contact with the lubricating fluid, the lubricating fluid concentrates in the narrow gap 64 at both ends due to surface tension, and the central wide gap 65 becomes an air passage. In FIG. 6, the circulation path 1f that circulates to the unbalanced herringbone groove 1b is formed from the narrow gap 64, so that the lubricating fluid passes through the recess channel 1e, the narrow gap 64, and the circulation path 1f. To recirculate.

  In the lower part of FIG. 6, a sleeve end face constituted by an inner cylinder 61 and an outer cylinder 62 is shown, and a narrow gap portion 64, a wide gap portion 65, and a recessed channel 1e are shown.

  Since the narrow gap portion 64 continues to the upper end surface of the sleeve, there is a possibility that the lubricating fluid may ooze out from the upper end surface of the sleeve. If the amount is of concern, it can be avoided by applying an oil repellent agent near the upper end of the sleeve of the narrow gap portion 64, or filling the narrow gap portion 64 near the upper end of the sleeve with a relatively high viscosity adhesive. For further completeness, a sealing plate 63 is used.

  The sealing plate 63 is a transparent thin plate and is disposed so as to cover the gap between the inner cylinder 61 and the outer cylinder 62 at the upper end surface of the sleeve. 7, the sealing plate 63 has a circular hole 71 having a diameter of about 0.3 mm or more at a position corresponding to the wide gap portion 65 of the gap portion. The circular hole 71 forms a seal portion due to surface tension to prevent the lubricating fluid from bleeding out. Since the sealing plate 63 is a transparent plate, the lubricating fluid in the narrow gap portion 64 can be visually recognized, and the amount of the lubricating fluid can be known from the position of the boundary.

  The management of the minimum gap of the access hole 1h in the first and second embodiments is important from the viewpoint of sealing the lubricating fluid, and there is a possibility that a member for adjusting the gap is required. If a gap is provided between the inner cylinder 61 and the outer cylinder 62 as in the present embodiment, the minimum gap in the gap can be easily set and managed to about 0.1 to 0.2 mm, and lubrication can be achieved. The fluid sealing ability can be improved.

  The structure in which the sleeve is formed as a double cylinder as described above and the circulation path and the vent hole are formed as a gap therebetween facilitates the size control of the gap portion, but the outer diameter of the inner cylinder 61 and the inner diameter of the outer cylinder 62 are controlled. It requires precision and can increase costs. The outer cylinder 62 is made of resin, and the inner cylinder 61 and the outer cylinder are made smaller by making the inner diameter of the outer cylinder 62 slightly smaller than the outer diameter of the inner cylinder 61 and utilizing the elasticity of the outer cylinder 62 or the temperature expansion difference therebetween. It can be improved by assembling 62. In that case, instead of forming a gap portion by making a part of the outer peripheral surface of the inner cylinder 61 flat, the gap portion may be formed on the inner peripheral surface of the outer cylinder 62 by molding.

  FIGS. 8 and 9 are views for explaining a fourth embodiment of the present invention, and show a longitudinal sectional view of a hydrodynamic bearing motor and a detailed structural view of a counter plate, respectively. 1 differs from the first and second embodiments in the sleeve structure and the vicinity of the shaft end, and differs from the third embodiment shown in FIG. 6 in the circulation path structure in the vicinity of the shaft end. Will be explained. 8 and 9, the same number is assigned to the same shape as in FIGS.

  In particular, the difference between FIG. 6 and FIG. 8 is the sleeve end and the counter plate structure, and the recessed channel 1e provided on the sleeve end surface is provided on the counter plate 83 side. In FIG. 8, the sleeve is composed of an inner cylinder 81 and an outer cylinder 82, and it is the same that a narrow gap portion 64, a wide gap portion 65 and a circulation hole 1f are provided between them. The counter plate 83 is made thicker than the counter plate 13 of FIG. The counter plate 83 is formed with a circular recess 85 that accommodates the shaft 11 as an extension of the inner peripheral surface of the sleeve inner cylinder 81, and a recess channel 84 is formed so as to be connected to the circular recess 85 and the narrow gap portion 64. . In FIG. 8, the recessed channel 84 is formed in two places. In the lower part of FIG. 8, reference numeral 86 denotes a boundary between the inner cylinder 81 and the outer cylinder 82, reference numeral 64 denotes a narrow gap portion, and reference numeral 65 denotes a position where the wide gap portion contacts the surface of the counter plate 83.

  9A is a plan view of the counter plate 83, and FIG. 9B is a sectional view of the opening of the recessed channel 84 indicated by A-A 'in FIG. 9A. Reference numeral 91 denotes an opening of the recessed channel 84, and reference numeral 92 denotes a cross-sectional shape of the opening 91.

  The operation principle is the same as that of the third embodiment shown in FIG. The method of forming the circular recess 85 and the recess channel 84 in the counter plate 83 is the same as the processing of the recess channel 1e in FIG. 6, and the processing is easier than in the case of FIG. 6 because it is formed on the counter plate 83 thinner than the sleeve. It is easy to get accuracy.

  In the first, second and third embodiments, a considerable part of the floating force of the rotating part is due to the ability of the radial bearing 1b to pump the lubricating fluid in the axial direction and the variable opening near the axial end. Depends on the generated lubricating fluid pressure. As can be easily understood from the operating principle, the axial rigidity to be kept in a predetermined floating position range when the rotating part receives vertical acceleration is considered separately from the contribution of the spiral groove 1c near the shaft end. It is proportional to [aperture area change amount] / [shaft end position change amount]. Therefore, in order to ensure the floating position accuracy of the rotating part in realizing the present invention, [aperture area change amount] / [shaft end position change amount] is a predetermined value near the predetermined floating position of the rotating part. The opening shape of the recessed channels 1e and 84 is set so that the opening portion breaks when the shaft end further moves upward from the predetermined flying position and moves upward in FIGS. In this configuration, the area rapidly increases.

  In FIGS. 1 and 6, the recessed channel 1e is formed by carving from the sleeve end face side. In this case, it is necessary to reduce the width at the surface of the recessed channel 1e and increase the width at the back. Of course, such processing can be realized by etching, sputtering or other fine processing techniques. However, when changing the [opening area change amount] / [shaft end position change amount] at each floating position of the rotating portion to precisely control the rotating portion floating position, the opening portion of the recessed channel 1e is used. Although there is a demand for more precise formation of the cross-sectional shape, current micromachining technology has its limitations. The fourth embodiment shown in FIGS. 8 and 9 is a structure effective in such a situation. That is, the concave channel 84 is formed on the surface of the counter plate 83, and the cross section of the opening 91 is formed with a large width on the surface and a small width on the back as indicated by reference numeral 92, so that the above condition is satisfied. In this case, the cross-sectional shape control process is easier than in the case of FIGS. The counter plate 83 can be easily manufactured by a precision press or a resin precision mold.

  In the description of the above embodiment, the circulation path opening is arranged on the outer periphery of the shaft end portion, and the shaft end groove is constituted by a pump-in spiral groove. This is a configuration in which mutual interference is reduced so that the spiral groove at the end of the shaft exhibits its maximum capability and load capacity control by an orifice or a variable opening in the circulation path is facilitated.

  From the first embodiment to the fourth embodiment, all the hydrodynamic fluid bearing motors have been described with respect to specific structural examples and operating principles of the present invention by taking the shaft rotation structure as an example. However, it is apparent that the present invention can be applied to a structure in which the shaft is fixed and the sleeve side is rotationally driven within the scope of the present invention. However, if there is a circulation path on the sleeve side, centrifugal force is applied to the lubricating fluid in the circulation path, and the possibility of lubricating fluid leakage is higher than that of the shaft rotation structure.

  Further, in the above embodiment, the thrust bearing is described as a spiral groove at the end of the shaft, and the operation principle and effect have been described. However, it is clear that the thrust bearing can be applied to other structures such as a structure in which the thrust bearing is formed on the sleeve end surface. It is effective to reduce sliding wear quickly.

  Although the entire structure of the magnetic disk drive using the hydrodynamic bearing motor of the above embodiment was not shown, the vertical cross-sectional structure of the hydrodynamic bearing motor that almost determines the vertical cross-sectional structure of the magnetic disk drive was shown. Thus, the thin structure of the magnetic disk device is defined. Thus, in the present embodiment, it was shown that the floating rotation of the rotating part including the magnetic disk can be supported with high accuracy without having a thrust bearing larger than the shaft diameter. By using the hydrodynamic bearing motor, a thin and low power consumption magnetic disk device can be realized.

  The operation principle and structure of the present invention have been described with reference to the embodiments. In the above embodiment, only a few examples are given to explain the operation principle of the present invention, and it is needless to say that the materials and structures can be modified without departing from the spirit of the present invention. For example, since air bubbles in the lubricating fluid can be removed at the air vent part following the circulation hole adopted in the above embodiment, the lubricating fluid is injected at atmospheric pressure and deaerated by rotating for a predetermined time. It is also possible to adopt such a process. Furthermore, it is possible to extend the time during which the hydrodynamic fluid bearing motor and the magnetic disk device can be moved by exchanging the lubricating fluid during use and adding the lubricating fluid by using these access holes.

  According to the hydrodynamic bearing motor of the present invention, it is possible to realize a hydrodynamic bearing motor capable of precisely controlling the flying height of the rotating portion without having a thrust bearing larger than the shaft diameter. Since the flow rate of the lubricating fluid can be kept to a minimum, the possibility of lubricating fluid leakage is reduced and axial loss is reduced. Furthermore, in the present invention, since the bubbles in the lubricating fluid can be removed during rotation, the assembling process is simplified and the cost can be reduced. It is particularly suitable for a thin and low current consumption magnetic disk device.

The longitudinal cross-section and sleeve end surface of the hydrodynamic bearing motor which is a 1st Example are shown. The end surface of the sleeve 12 in FIG. 1 and the edge part of the axis | shaft 11 are shown. The sleeve 12 in FIG. 1 is divided vertically and shown as a perspective view. The figure for demonstrating the floating position of a rotation part in a 1st Example is shown. The figure for demonstrating the floating position of a rotation part in 2nd Example is shown. The longitudinal cross-section and sleeve end surface of the hydrodynamic bearing motor which is a 3rd Example are shown. The structure of the sealing board 63 in FIG. 6 is shown. The longitudinal cross-section and counterplate of the hydrodynamic bearing motor which are the 4th Example are shown. The details of the shape of the counter plate in FIG. 8 are shown. A structure described in Japanese Patent Publication No. 48-004498 is shown as an example of the prior art. As an example of the prior art, the structure described in JP-A-58-024616 is shown.

Explanation of symbols

11 ... shaft, 12 ... sleeve,
13 ... Counter plate, 14 ... Hub,
15 ... Base plate, 16 ... Rotor magnet,
17 ... stator core, 18 ... coil,
19: Magnetic piece,
1a, 1b .. unbalanced herringbone groove,
1c... Spiral groove, 1d, 1f .. circulation hole,
1e: recessed channel, 1g: interface of lubricating fluid,
1h ... access hole, 1j ... seal part,
1k ...
21 ... Opening, 22 ... Center of shaft end,
23 ... The center of the spiral groove,
31 ... Rotation direction of the shaft 11,
41 ... first axial load capacity, 42 ... second axial load capacity,
43 ... Sum of first and second axial load capacities,
44: Value obtained by adding the rotating part weight to the magnetic attractive force,
45... Value obtained by subtracting the rotating part weight from the magnetic attractive force,
61 ... Inner cylinder, 62 ... Outer cylinder,
63 ... sealing plate, 64 ... narrow gap,
65 ... wide gap part,
71 ... round hole,
81 ... inner cylinder, 82 ... outer cylinder,
83 ... counter plate, 84 ... recessed channel,
85 ... circular recess, 86 ... boundary between the inner cylinder 81 and the outer cylinder 82,
91: Opening of recess channel 84, 92: Cross-sectional shape of opening,
101 ... cylindrical shaft, 102 ... sleeve,
103 ... spiral groove, 104 ... tip
105 ... pressure chamber, 106 ... circulation path,
107 ... opening,
111 ... cylindrical shaft, 112 ... sleeve,
113 ... ball, 114 ... circulation path,
115 ... Opening, 116 ... Pressure chamber

Claims (12)

A cylindrical shaft having a shaft end surface substantially orthogonal to the axial direction at least near the outer periphery, a bottomed sleeve that is rotatably fitted relative to the shaft, and a lubricating fluid filled in the space between the shaft and the sleeve; A hydrodynamic bearing motor having a magnetic means for generating a magnetic attractive force between a shaft and a sleeve, and having a pumping capability of lubricating fluid in the axial direction on the shaft surface or the inner peripheral surface of the sleeve The sleeve has an unbalanced herringbone groove and has a circulation path in the sleeve connecting the vicinity of the shaft end and the side far from the shaft end of the unbalanced herringbone groove, and the opening of the circulation path is provided near the bottom of the bottomed sleeve. Then, the channel area is changed in cooperation with the shaft end that moves in the axial direction with rotation, and the minimum value of the channel area is defined by the gap between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. Lubricating fluid as a smaller channel cross-sectional area A variable opening with a substantially variable entrance area is constructed. During rotation, the unbalanced herringbone groove generates radial bearing dynamic pressure to maintain the rotating part posture and pumps the lubricating fluid in the axial direction. An axial load capacity for supporting the rotating part in the axial direction is obtained by increasing the lubricating fluid pressure in the vicinity of the shaft end by the pumped lubricating fluid and the variable opening, and the magnetic attractive force and the gravity applied to the rotating part and the axial direction are obtained. A hydrodynamic bearing motor that balances the load capacity and precisely controls the flying height of the rotating part without having a thrust bearing larger than the shaft diameter. 2. The hydrodynamic bearing motor according to claim 1, wherein the bottomed sleeve is composed of a cylindrical sleeve material and a counter plate fixed to the end surface of the cylindrical sleeve material, and a circulation path near the shaft end is provided on the end surface of the cylindrical sleeve material. The recessed channel is formed by etching, laser processing, electric discharge processing, electrolytic processing, ion milling or cutting processing, which is a fine precision processing technique, to ensure the position and dimensional accuracy of the opening. Hydrodynamic bearing motor, which makes it easy to control the precise flying height of the rotating part 3. The hydrodynamic bearing motor according to claim 2, wherein the opening shape of the recessed channel provided in the sleeve end surface on the inner peripheral surface of the sleeve is formed to have a large opening width at a position away from the sleeve end surface in the axial direction. The hydrodynamic bearing motor is characterized by improving the axial rigidity at the time of floating of the rotating part and facilitating precise floating amount control of the rotating part. 2. The hydrodynamic bearing motor according to claim 1, wherein the bottomed sleeve comprises a cylindrical sleeve material and a counter plate fixed to the end surface of the cylindrical sleeve material, and the counter plate is an extension of the inner peripheral surface of the sleeve. A circular recess having substantially the same inner diameter and a recess channel connected to the circular recess, and the circular recess and the recess channel are etching, laser processing, electric discharge processing, electrolytic processing, or ion milling, which are fine precision processing techniques. Alternatively, the hydrodynamic bearing motor is characterized in that it is formed on the counter plate surface by pressing, molding or cutting to ensure the position and dimensional accuracy of the opening and to facilitate the precise control of the flying height of the rotating part. 5. The hydrodynamic bearing motor according to claim 4, wherein the opening shape facing the axis of the recessed channel provided in the counter plate has a large opening width on the surface and a small opening width at a position separated in the axial direction. The hydrodynamic bearing motor is characterized in that the precision in the axial direction at the time of floating of the rotating part is improved and the precise floating amount control of the rotating part is facilitated. 2. The hydrodynamic bearing motor according to claim 1, wherein a pump-in spiral groove is provided at the shaft end or the bottom of the sleeve, and an axial load capacity that is substantially inversely proportional to a distance between the shaft end and the bottom of the sleeve is set near the shaft end. Hydrodynamic bearing motor characterized by increased axial rigidity of rotating part support 7. The hydrodynamic bearing motor according to claim 6, wherein the maximum value of the axial load capacity generated by the pumped lubricating fluid and the substantially variable opening is not less than the value obtained by adding the weight of the rotating part to the magnetic attraction force. It is possible to control the flying height by ensuring the rotation of the rotating part in any of the upright, inverted, and horizontal positions without a bearing with a small diameter shaft and larger than the shaft diameter. Hydrodynamic bearing motor characterized by 7. The hydrodynamic bearing motor according to claim 6, wherein the maximum axial load capacity generated by the pumped lubricating fluid and the substantially variable opening is a value obtained by subtracting the weight of the rotating part from the magnetic attraction force and the magnetic attraction Set between the values obtained by adding the weight of the rotating part to the force to maximize the axial rigidity of the spiral groove in any of the upright, inverted, and horizontal positions without bearings larger than the shaft diameter. A hydrodynamic bearing motor that contributes to precise flying height control of the rotating part. 2. The hydrodynamic bearing motor according to claim 1, wherein the lubricating fluid is connected to the circulation path so that the lubricating fluid gradually forms a gap so as to form an interface with the air, and the lubricating fluid in the gap between the shaft and the sleeve is held. A hydrodynamic bearing characterized by having a vent hole that has a taper seal portion and communicated with the atmosphere, and that bubbles in the lubricating fluid are released to the atmosphere by the vent hole in the process of circulating the lubricating fluid in the circulation path. motor 10. The hydrodynamic bearing motor according to claim 9, wherein the lubricating fluid is connected to a circulation path in the sleeve, and a vent hole outlet is provided on the sleeve end face to provide an access hole for the lubricating fluid. Hydrodynamic bearing motor capable of level monitoring and lubrication fluid injection 11. The hydrodynamic bearing motor according to claim 10, wherein the sleeve has a double cylinder configuration of an inner cylinder and an outer cylinder, and the outer peripheral surface of the inner cylinder is partially flat, or the inner peripheral surface of the outer cylinder is provided with a recess. As a result, an axial gap is formed between the outer peripheral surface of the inner cylinder and the inner peripheral surface of the outer cylinder. The narrow gap portion in the gap cross section is circulated and the wide gap portion in the gap cross section is vented. Hydrodynamic bearing motor characterized in that it has an access hole to the lubricating fluid as a part 12. The hydrodynamic bearing motor according to claim 11, wherein the sleeve is exposed to a sleeve end face with a sealing plate having a circular opening having a diameter equal to or smaller than a gap of a wide gap portion formed between an inner cylinder and an outer cylinder of the sleeve. The hydrodynamic bearing motor is characterized in that the gap is sealed to prevent leakage of the lubricating fluid.

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