JPH03159537A - Rotor and bearing structure therefor - Google Patents

Abstract

PURPOSE:To improve rotary performance of a motor by supporting a rotary shaft on a supporting shaft and a fixing base through two dynamic pressure bearings and further supporting the rotary shaft through a rolling bearing. CONSTITUTION:A fixed side member 3a constituting a thrust bearing 3 is arranged on a fixing base 1 separated from the outer circumference of a supporting shaft a. A fixed side member 4a constituting a radial bearing 4 is fixed to the outer circumferential section of the supporting shaft 2. A supporting member 6 is supported by a ball bearing 9, one type of rolling bearing; fixed to the supporting shaft 2 at the canopy part, and a circular shaft member 7 is secured to the lower end part. The lower end part of the shaft member 7 provides the movable side member 3b of the thrust bearing 3 and the inner circumferential face thereof provides the movable side member 4b of the radial bearing 4. The radial bearing 4 and the thrust bearing 3 constitute dynamic pressure bearings respectively. When the dynamic pressure rolling bearing is additionally employed, rotary performance is improved and starting torque can be reduced regardless of the attitude.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a shaft fj: structure in which the radial bearing and the thrust bearing are composed of fluid dynamic pressure bearings, and the vibration during rotation is small and high-speed rotation is possible. Regarding the rotating body and its bearing structure suitable for spindle motors, etc., it is particularly suitable for driving laser scanner motors and hard disk drivers (hereinafter referred to as 'HDDJ' in cars), etc., which have good rotational performance regardless of the orientation of the motor. The present invention relates to a rotating body suitable for a spindle motor and its bearing structure.

[Prior art and problems to be solved by the invention] In recent years, H
In order to increase the storage capacity and reduce power consumption of DDs, there is a demand for a spindle motor for driving the DDs, which has a higher performance and is more suitable for this purpose.

FIG. 5 is a partial sectional view of a conventional HDD spindle motor, in which a shaft support tube 22 is provided in the center of a mounting base 21, and a stator coil group 23 is provided on the outer periphery of the shaft support tube 22.
is fixed, and a rotary shaft 25 is rotatably supported on the inner periphery via a ball bearing 24. Rotating axis 2
A support member 27 for mounting and fixing a hard disk on the outer circumferential surface is fixed to the upper end of the hard disk drive 5 . A rotor magnet group 28 is fixed to the inner circumferential surface of the support member 27 so as to face the stator coil group 23 .

In the spindle motor that uses a ball bearing as the bearing, the magnitude of vibration of the spindle motor depends on the gap between the ball bearings. Vibration in the radial direction depends on the radial gap between the ball bearings, and vibration in the thrust direction depends on the thrust gap between the ball bearings. They are about the same level, and measures such as applying preload to the ball bearings have been taken to reduce this gap, but runout in the radial direction is a non-repetitive component and the O. S is about microns, which is not a satisfactory value. Moreover, if such a preload is applied to the ball bearing, the torque of the motor increases and goes against the goal of reducing the power consumption of HDDs. Therefore, as long as the above-mentioned ball bearings are used, it is practically impossible in principle to further reduce the vibration of the spindle motor. Furthermore, the rotational speed of scanner motors used in laser printers and the like tends to increase year by year, and conventional bearing structures using ball bearings are no longer able to handle this.

Therefore, a spindle motor using a fluid dynamic bearing has been proposed to achieve higher rotational performance.

FIG. 6 is a cross-sectional view of a spindle motor using a dynamic pressure bearing for which the present applicant applied for a patent prior to this application. Mounting stand 3
A support shaft 32 is erected at the center of the support shaft 1, and an annular thrust plate 33 is fixed to the mounting base 31, and a cylindrical radial bearing 34 is fixed concentrically with the support shaft 32. A plurality of stator coils 35 are fixed at equal intervals above the cylindrical radial bearing 34 of the support shaft 32. The support member 36 is in the shape of a horn, and the upper canopy part is loosely fitted above the support shaft 32, and the annular shaft member 37 with an L-shaped cross section is fixed to the lower canopy part. There is. The lower end of the shaft member 37 faces the thrust plate 33 and the inner circumferential surface faces the radial bearing 34, forming a savial groove dynamic pressure thrust bearing and a herribone groove dynamic pressure radial bearing. A plurality of rotor magnets 38 are fixed at equal intervals at positions facing the inner stator coil 35 of the support member 36.

When current sequentially flows through the stator coil 35, the support member 36 equipped with the rotor magnet 38 starts rotating, and the air dynamic pressure thrust bearing between the upper surface of the thrust plate 33 and the lower surface of the shaft member 37 is connected to the outer peripheral surface of the radial bearing 34 and the shaft. The inner peripheral surface of the member 37 constitutes an air dynamic pressure radial bearing. Therefore, since the shaft member 37 is supported without solid contact, it can handle smooth and high-speed rotation, and problems such as friction and vibration are solved compared to those using conventional ball bearings. be done.

However, when the above-mentioned spindle motor is also operated in a horizontal position (in a direction in which the direction of gravity is perpendicular to the motor axis), a radial moment is generated due to the gravity of rotation, and the radial axis is affected by the radial bearing. is tilted, and the rotating part is pressed against the bearing in a state where the radial unbalance between the rotor magnet and the stator coil becomes larger. Also, since the bearing side is made up of a separate piece, it was difficult to achieve a right angle during assembly.

In addition to the above-mentioned problems, when a conventional spindle motor using a dynamic pressure bearing is used in a horizontal position, the following problems occur.

■When using two separate hydrodynamic bearings, when assembling,
It was difficult to adjust the concentricity, and the clearance between the radial bearing and the shaft was on the order of microns, so matching the clearance between the two shaft centers was a problem in the manufacturing process. Furthermore, if the thrust bearings are two separate bearings, there is no adjustment of the relative position between the thrust bearings. In addition, the thrust collar of a thrust bearing is usually made within a few microns of parallelism, and it is necessary to suppress it to a fraction of this when setting, which makes it difficult.

■In addition, in a radial gear type spindle motor as shown in Figure 6, a moment is generated due to the unbalance of magnetic force in the radial direction between the rotor magnet and the stator coil, causing the radial axis to tilt with respect to the main shaft, and the dynamic pressure surface to The starting torque increased due to uneven contact.

The present invention has been made in view of the above-mentioned points, and eliminates the above-mentioned problems by using a fluid dynamic pressure bearing and a rolling bearing as a bearing.
The object of the present invention is to provide a rotating body and its bearing structure suitable for spindle motors and the like, which have good rotational performance and require a small starting torque regardless of the orientation in which they are used.

[Means to solve the problem]

In order to solve the above problems, the present invention has a bearing structure configured as follows.

The mounting base includes a support shaft that stands upright in the center of the mounting base, and a rotating part that has a support shaft penetration hole in the center through which the support shaft is pushed through, and the rotating part is supported by the support shaft via a radial bearing. The radial bearing and the thrust bearing are each hydrodynamic bearings, and the rotating part is supported by the support shaft via a rolling bearing.

In addition, at least one or a part of the fixed side member and movable side member constituting the radial bearing, the fixed side member and movable side member constituting the thrust bearing, and the support shaft are made of a ceramic material, or the thrust bearing and the movable side member constitute the thrust bearing. A ceramic material layer or a thin film coated with a material different from the base material or a surface-altered layer formed by altering the base material is provided on the mutually opposing sliding surfaces of the fixed side member and the movable side member of the bearing. Moreover, it is characterized in that the ceramic is silicon carbide or alumina.

Further, the thrust bearing is characterized in that it is preloaded by magnetic force in a direction opposite to the direction in which dynamic pressure is generated in the thrust bearing.

Another feature is that an elastic pad made of silicone rubber or the like is interposed between the fixed side member constituting the thrust bearing and the mounting base.

Moreover, a rotating body comprising the bearing structure described in any one of the above.

Further, a rotor magnet or a rotor magnetic body is disposed on the rotating part, and a stator filter is disposed on the stationary side in correspondence with the rotor magnet or rotor magnetic body, thereby forming a spindle motor.

[Effect]

By configuring the bearing structure to use both a hydrodynamic bearing and a rolling bearing as described above, the rotating part rotates while being supported by the rolling bearing when it is stopped and rotates at low speed, so the startup and initial rotational torques are reduced. In addition, since it rotates while being supported by the hydrodynamic bearing during high-speed rotation, it provides the high-performance rotational characteristics that are characteristic of hydrodynamic bearings, and the radial bearing can be shortened, so when used as a spindle motor, the motor drive unit You can take up a lot of space for the installation.

Furthermore, by applying a preload in the thrust direction using magnetic force, the inclination of the radial shaft with respect to the radial bearing is corrected, eliminating uneven contact and further reducing the starting torque.

Further, the rotating part can be stably rotated without being thrown out by dynamic pressure in the thrust direction. Particularly when used in a spindle motor, even if the spindle motor is used in a horizontal position, the motor rotating portion C rotates stably.

In addition, at least one or a portion of the fixed side member and movable side member constituting the radial bearing, the fixed side member and movable side member constituting the thrust bearing, and the support shaft may be made of ceramic or plastic material with excellent wear resistance. Ceramic material with excellent abrasion resistance on the mutually opposing sliding surfaces of the fixed side member and the movable side member. Since the surface has a modified τK layer, it can be used without or with minimal lubrication, and the starting torque and f′
Load torque can be reduced.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view of a spindle motor using a bearing structure according to the present invention. A support shaft 2 is provided upright in the center of the mounting base 1. An annular stationary member 3a constituting the thrust bearing 3 is disposed on the mounting base 1 at a predetermined distance from the outer periphery of the support shaft 2 with an elastic pad 10 made of an elastic body interposed therebetween. Furthermore, a cylindrical stationary member 4a constituting the radial bearing 4 is fixed to the outer peripheral portion of the support shaft 2. A plurality of stator coils 5 are fixed to the upper part of the movable member 4a of the support shaft 2 at equal intervals.

On the other hand, the support member 6 has a cap shape, the upper canopy part is supported by a ball bearing 9 which is a type of rolling bearing attached to the support shaft 2, and the lower end part has a cross section L.
A letter-shaped annular Ipth material 7 is fixed. The lower end of the shaft member 7 is a movable side member 3b facing the fixed side member 3a of the thrust bearing 3, and its inner peripheral surface is a movable side member 4b facing the fixed side member 4a of the radial bearing 4. It has become. The fixed side member 3a and the movable side member 3b constitute a radial full dynamic pressure thrust bearing 3, which will be described in detail later, and the fixed side member 4a and the movable side member 4b constitute a herringbone groove dynamic pressure radial bearing 4, which will be described in detail later. Configure.

Furthermore, a plurality of rotor magnets 8 are fixed at equal intervals on the inner periphery of the support member 6 at positions facing the stator coil 5. When the stator coil 5 is sequentially energized with Tft, the support member 6 (motor rotating part) equipped with the rotor magnet 8 starts rotating, and this support member 6 is connected to the fixed side member 3a and the movable side member 3b of the thrust bearing 3. The air dynamic pressure generated between the fixed side member 4a and the movable side member 4b of the radial bearing 4 allows the shaft to be supported without any solid contact, allowing for smooth and high-speed rotation. Compared to those using ball bearings, problems such as friction and vibration are eliminated.

The annular bearing member 7 of the fixed side member 4a of the radial bearing 4 (
A dynamic pressure generating groove for generating dynamic pressure, such as a herringbone-shaped groove C as shown in FIG. 2, is formed on the surface facing the movable side member 4b).
A dynamic pressure generating groove for generating dynamic pressure, such as a spiral groove C shown in FIG. 3, is formed on the surface facing the annular bearing member 7 (movable side member 3b) of a.

The dynamic pressure generating grooves are formed on the inner peripheral surface (movable side member 4b) and lower end surface (movable side member 3b) of the annular shaft member 7, and on the upper surfaces of the fixed side member 4a and the fixed side member 3a facing the same. It may be smooth.

In the spindle motor having the above configuration, when the stator coil 5 is sequentially energized, the support member 6 to which the rotor magnet 8 is fixed starts rotating at the center of the ball bearing 9.
At the same time, the fixed side member 3a and the movable side member 3 of the thrust bearing 3
Air dynamic pressure is generated between b. Furthermore, air dynamic pressure is generated between the fixed side member 4a and the movable side member 4b of the radial bearing 4. Further, when the rotational speed of the support member 6 increases and the rotation becomes high speed, the dynamic pressure increases, the bearing clearance of the dynamic pressure bearing becomes uniform, and the concentricity between the support member 6 and the support shaft 2 increases. That is, at the initial stage of rotation of the support member 6, where the bearing clearance of the hydrodynamic bearing is not uniform, the support member 6 rotates with a ball bearing, and during high-speed rotation, the annular shaft member 7 (movable side member 3b and movable side member 4b) rotates with the fixed side member 3a. Since it is pivoted without solid contact with the stationary side member 4a, it can handle smooth and high-speed rotation. Therefore, the problems of friction and vibration in the conventional spindle motor using only ball bearings can be solved.

In the spindle motor having the configuration described in 42 above, the fixed side member 4a and the movable side member 4b that constitute the dynamic pressure radial bearing 4 and the fixed side member 3a and the movable side member 3b that constitute the thrust bearing 3 generate dynamic compression air during rotation. Because these bearings rotate without contact, the parts that make up these bearings can be made of any material that can be processed with high precision, and common metal materials and organic materials can be considered. The problem is to reduce frictional resistance and wear during startup and low-speed rotation, and the range of materials that can generally be used depends on the bearing structure.

In this embodiment, the ball bearing 9 is used in combination with the hydrodynamic bearing, so that the frictional resistance of the hydrodynamic bearing at the time of startup is reduced, and the magnetic force of the rotor magnet 8 is used to reduce the dynamic pressure of the thrust bearing. Since it is preloaded in the opposite direction, it has a structure that prevents uneven hitting. Therefore, the range of materials that can be used for bearings is wide. Here, the method of preloading is to shift the magnetic center of the rotor magnet 8 upwards with respect to the magnetic center of the stator coil 5, that is, by a predetermined amount d in the direction opposite to the thrust bearing, or to shift the magnetic center of the rotor magnet 8 by a predetermined amount d to This is done by typing. The fixed flll that constitutes the thrust bearing 3
I1 member 3a and movable side member 3b (annular bearing member 7),
If either or both of the fixed side member 4a and the movable side member 4b (annular bearing member 7) that constitute the radial bearing 4 are made of stainless steel, a thin layer of lubricant can be applied to the contact surface of the bearing. , stable performance can be obtained over a long period of time.

It is also necessary to reduce the load torque, and in this case, a ceramic material with particularly excellent wear resistance is preferable. Among them, carbon silicon and alumina are preferred.

In addition, the substrate is coated with a thin film of a material different from the substrate, or a surface-altered layer is provided by altering the substrate. This thin film can be formed by physical vapor deposition, chemical vapor deposition or plating. This thin film is usually made of a different material from the base material. For example, the base material is stainless steel and the coating material is ceramic. However, the same type of material as the base material may be used.

For example, some types of nickel plating become denser and harder than the base material. Moreover, the smoothness can be improved. ``The base material is a different material'' shall include such cases. Further, the surface altered layer can be formed by, for example, oxidation relaxation, nitriding treatment, or ion implantation.

In addition, in order to ensure the right angle between the radial dynamic pressure bearing and the thrust dynamic pressure bearing during assembly, the mounting base 1 and the thrust bearing 3
An elastic pad 10 made of an elastic body is placed between the fixed side member 3a of
By interposing the elastic pad 10 with an alignment function, the perpendicularity can be easily achieved. The elastic pad 10 may be made of any elastic material, but an easily available material such as silicone rubber is preferred.

The spindle motor is a so-called synchronous motor type in which a plurality of stator coils 5 are arranged at equal intervals around the outer periphery of the support shaft 2, and rotor magnets 8 corresponding to the stator coils 5 are arranged on the inner periphery of the support member 6. However, the spindle motor is not limited to a synchronous motor type, but may be an induction motor type. In that case, instead of the rotor magnet 8, a plurality of rotor magnetic bodies such as a rotor core are arranged at equal intervals.

FIG. 4 is a conceptual diagram of a bearing structure according to the present invention. now,
If the major axis of the fixed side member 41 of the hydrodynamic radial bearing is Dd, the length is Ld, the clearance Cd between the fixed side member 41 and the movable side member 42, and the distance between the centers of the ball bearing 43 and the fixed side member 41 is B, When used in a vertical position, for example, CD
is several microns, B/L=1, L/D=1, if you use a bearing with a ball bearing 43 radial clearance cb of about 5 microns, it will rotate supported by the ball bearing 43 at startup. confirmed. In order to rotate while being supported by the ball bearing during startup, the diameter and radial clearance of the ball bearing, the radial outer diameter of the dynamic pressure radial bearing, the radial clearance and radial length, and 21! It depends on the relative distance of the bearing I, and any configuration that satisfies the C-order relational expression according to the present invention may be used.

Cb<(2Cd/Ld)XB Furthermore, when used in a horizontal position, by applying a magnetic bridle, it can be used under the same conditions as in a vertical position.

As mentioned above, the starting torque can be easily reduced by using Hakamatoru's rolling bearings (although the structure uses two bearings, one of the forces is the rolling bearing, so assembly is difficult. It becomes easier.

Although the above embodiment shows an example in which the bearing structure of the present invention is used in a spindle motor, the bearing structure of the present invention is not limited to spindle motors, but is applicable to rotating bodies that rotate at high speed with little vibration. It can be widely used as a bearing structure.

〔Effect of the invention〕

As explained above, according to the present invention, the following excellent effects can be obtained.

(1) The following parameters that determine the bearing structure: The major axis, length, clearance of the fixed side member that makes up the hydrodynamic radial bearing, and the distance between the centers of the rolling bearing and the radial bearing. Starting torque can be reduced by using a rolling bearing with a corresponding radial clearance. (2) Even though a rolling bearing is used, the high characteristics of a hydrodynamic bearing can be achieved during rotation.

(3) Since one of the bearings is a rolling bearing, it is easy to increase the dimensional accuracy during assembly.

(4) By applying a sudden thrust in the thrust direction,
Uneven bearing contact can be prevented and starting torque can be further reduced.

Furthermore, during rotation, the presence of a force that counteracts the dynamic pressure stabilizes the rotation. In particular, when used in a horizontal position, the motor rotating part rotates stably without jumping out due to dynamic pressure in the thrust direction. (5) In radial bearings and thrust bearings, at least one or a part of the constituent members and support shafts are made of a ceramic material, or the mutually opposing sliding surfaces of each constituent member have a ceramic material layer or a material different from the base material. By providing a thin film coated with or a surface modified layer formed by modifying the base material, it can be used without or with minimal lubrication.

(6) By interposing an elastic pad between the thrust bearing and the fixed side, the perpendicularity between the radial and thrust of the dynamic pressure bearing can be easily realized.

[Brief explanation of the drawing]

1 (50 is a sectional view of a spindle motor using the bearing structure according to the present invention, FIG. 2 is a diagram showing an example of a dynamic pressure generating groove formed in a radial bearing member, and FIG. 3 is a diagram showing an example of a dynamic pressure generating groove formed in a thrust bearing member. FIG. 4 is a sectional view showing a bearing structure according to the present invention, and FIG. 5 is a diagram showing an example of a conventional HDD.
FIG. 6 is a cross-sectional view of a spindle motor using a hydrodynamic bearing, for which a patent application was filed before the present application. In the figure, 1...Mounting base, 2...Support shaft, 3...
...Thrust bearing, 4...Radial bearing, 5...
・Stator coil, 6...Supporting member, 7...Annular shaft member, 8...Rotor magnet, 9...
Ball bearing, 10...elastic pad.

Claims (8)

[Claims] (1) The mounting base includes a support shaft erected in the center thereof, and a rotating part having a support shaft penetration hole in the center part into which the support shaft is inserted, and the rotating part is connected to the mounting base through a radial bearing. The rotating part is supported by the support shaft and also supported by the mounting base via a thrust bearing, the radial bearing and the thrust bearing are each hydrodynamic bearings, and the rotating part is supported by the support shaft via a rolling bearing. A bearing structure characterized by: (2) At least one or a part of the fixed side member and the movable side member that constitute the radial bearing, the fixed side member and the movable side member that constitute the thrust bearing, and the support shaft are made of a ceramic material, or Thrust bearings and radial bearings A ceramic material layer or a thin film coated with a material different from the base material or a surface-altered layer obtained by altering the quality of the base material is provided on the mutually opposing sliding surfaces of the fixed side member and the movable side member. The bearing structure according to claim (1). (3) The bearing structure according to claim 1 or 2, wherein the ceramic is silicon carbide or alumina. (4) Claim (1) characterized in that the thrust bearing is preloaded by magnetic force in a direction opposite to the direction in which dynamic pressure is generated.
The bearing structure according to any one of (3) to (3). (5) The bearing structure according to any one of claims (1) to (4), characterized in that an elastic pad is interposed between the fixed side member constituting the thrust bearing and the mounting base. (6) The bearing structure according to claim (5), wherein the elastic pad is made of silicone rubber. (7) A rotating body comprising the bearing structure according to any one of claims (1) to (6). (8) A rotor magnet or a rotor magnetic body is disposed on the rotating part, and a stator coil is disposed on the stationary side in correspondence with the rotor magnet or rotor magnetic body, thereby forming a spindle motor. A rotating body comprising the bearing structure according to claim 7.