Recently, in the field of information recording/reproducing apparatuses such as disk drive, efforts have been made to increase the capacity. For increasing the capacity, it is specially required to improve the rotational accuracy of the spindle motor for driving the disk used in the disk drive or the like. In order to meet the requirement for improving the rotational accuracy, there is an increasing trend of employing a hydrodynamic bearing in the spindle motor.
In a hydrodynamic bearing, there exists a hydrodynamic lubricant between a rotary side bearing and a fixed side bearing. The rotary side bearing and the fixed side bearing are provided with a dynamic pressure generating groove for inducing dynamic pressures to the hydrodynamic lubricant, which rotate the rotary body of the spindle motor via the hydrodynamic lubricant. That is, the spindle motor rotates in a state of being non-contact between the rotary side bearing and the fixed side bearing.
Thus, since the spindle motor rotates in a state of being non-contact, when a shock due to dropping or vibrating is applied thereto, the rotary side bearing or the rotary body moves from the fixed side bearing. In case the device is not configured so as to regulate the movement, the rotary body will slip off from the fixed side bearing. This means that the spindle motor is unable to display its function.
Accordingly, a slip-proof configuration is adopted in order to prevent the rotary body from slipping off from the fixed side bearing even when a shock due to dropping or vibrating is applied thereto.
A slip-proof configuration of a conventional fluid bearing motor will be described in the following.
As a fluid bearing motor, available are a fixed-shaft type and a rotary-shaft type.
In the fixed-shaft type, the fixed side bearing is a fixed shaft embedded in a chassis. The rotary side bearing is rotatable around the fixed shaft.
In the rotary-shaft type, the rotary side bearing is rotatably supported at the inner periphery of a cylindrical sleeve-like fixed side bearing fixed on a chassis.
First, the fixed-shaft type fluid bearing motor disclosed in Japanese Laid-open Patent H6-311695 is explained.
In this prior art example, a generally cylindrical fixed shaft is disposed upright. At the top of the fixed shaft is integrally formed an annular thrust plate projecting axially outwardly. On the other hand, the sleeve member which is a part of the rotary body is generally cylindrical which is increased in outer diameter at the top end. The inner periphery of the sleeve member includes a radial slide portion being generally cylindrical with a small diameter, a medium bore portion increased in diameter there above, and a large bore portion further increased in diameter above the medium bore portion.
The sleeve member is externally fitted on a fixed shaft from thereunder before the fixed shaft is securely set into a through-hole. An annular thrust holding plate is internally secured in a state such that the inner periphery is diametrically spaced apart against the fixed shaft in the large bore portion of the sleeve member. And, by the thrust holding plate and the sleeve member, a thrust plate is fitted in the annular recess of an opening diametrically outwardly formed at the inner side of the medium bore portion.
There is provided a herringbone groove at the annular portion of nearly the upper half of the radial slide portion of the sleeve member. A radial dynamic bearing is configured in that radial load pressures are generated by a liquid lubricant filled in the gap between the herringbone groove and the fixed shaft portion (radial receiver) opposing to the radial slide portion of the sleeve member.
Also, the upper and lower annular surfaces (axial receiver) of the thrust plate and the upper and lower annular surfaces (axial slide) of the annular recess respectively configure axial dynamic bearing portions. Herringbone grooves are formed along the entire peripheries of the upper and lower annular surfaces of the thrust plate, and high pressures are generated by the lubricant filled between the upper and lower annular surfaces of the annular groove, thereby forming an axial dynamic bearing portion.
In this way, it is configured in that the sleeve member or the like is able to freely rotate about the fixed shaft or the like via a lubricant. And, the displacement in a direction axial to the fixed shaft during rotation of the sleeve member can be sufficiently lessened by the axial dynamic bearing portions. Accordingly, even in case a shock is applied thereto, the sleeve member being a part of the rotary body will not slip off from the fixed shaft being a fixed side bearing.
Next, the shaft-fixed type fluid bearing motor disclosed in Japanese Laid-open Paten 2002-286038 is explained in the following.
In this prior art example, a shaft is externally fixed in a bracket. And, there are provided a disk-like upper thrust plate and lower thrust plate projected radially outwardly at the upper end and lower end of the shaft. There is a rotor which is provided with a sleeve supported by a shaft at the inner side thereof via a fine clearance for holding the lubricant. The sleeve is provided with an upper counter plate and lower counter plate in such manner as to cover the outsides of the upper thrust plate and the lower thrust plate. The upper and lower portions at the inner periphery of the through-hole of the sleeve are respectively formed with herringbone dynamic grooves by means of electrochemical machining. The underside of the upper thrust plate and the top of the lower thrust plate are respectively formed with spiral dynamic grooves by means of electrochemical machining. The portion ranging from the outer periphery of the shaft adjacent to the top of a gas-intervening portion disposed in the middle of the shaft to the underside of the upper thrust plate, the outer periphery thereof, and the outer periphery of the top surface thereof is formed with fine clearances against the portion ranging from the top of the through-hole at the inner periphery of the opposing sleeve to the underside of the upper counter plate, where the lubricant is retained.
In such a configuration, the radial dynamic bearing portion is configured with the upper and lower portions formed with the herringbone dynamic grooves at the inner periphery of the through-hole of the sleeve, the shaft opposing thereto, and the lubricant retained in the fine clearances. Also, the axial dynamic bearing is configured with (i) the underside of the upper thrust plate and the top of the lower thrust plate respectively formed with spiral dynamic grooves, (ii) the underside of the upper counter plate and the top of the lower counter plate respectively opposing thereto, and (iii) the lubricant retained in the fine clearances. The upper thrust plate and the lower thrust plate are held by the respective surfaces of the stepped portions of the sleeve respectively opposing to the underside of the upper thrust plate and the top of the lower thrust plate, and the underside of the upper counter plate and the top of the lower counter plate disposed in such manner as to cover the outsides of the upper and lower thrust plates.
In such a configuration, the displacement in a direction axial to the shaft during rotation of the sleeve can be lessened enough. Accordingly, even in case a shock is applied thereto, the sleeve being a part of the rotary body will not slip off from the shaft being the fixed side bearing.
Next, the rotary-type fluid bearing motor disclosed in Japanese Laid-open Patent H8-275447 is explained in the following.
In this prior art example, at the inner periphery of the cylindrical portion of a housing is disposed a sleeve having a projection at the outer periphery of the top end thereof. A motor rotates about a shaft fastened to the center of a rotor hub with a stopper fixed thereon. A thrust plate is caulked and secured to the bottom end of the sleeve fixed on the inner periphery of the housing, in which lubricating oil is filled as a fluid material. The thrust plate is formed with dynamic bearing grooves which are spiral grooves. The shaft is supported so as to be rotatable in a thrust direction due to dynamic pressure generated at the thrust plate and the shaft end as it rotates. Simultaneously, the shaft is supported so as to be rotatable in a radial direction as well due to dynamic pressure generated in the lubricating oil in a state of being non-contact with the sleeve.
When the rotor hub moves in a thrust direction, the stopper fixed on the rotor hub abuts the projection disposed at the sleeve. That is, it is configured in that the rotor hub will not slip off therefrom.
The motor assembling procedure is such that (i) a stator assembly with a coil-wound stator core fixed in a housing, (ii) a sleeve bearing assembly with a thrust plate fixed on a sleeve, and (iii) a rotor assembly with a shaft fixed on a rotor hub with a magnet are respectively manufactured. Subsequently, lubricating oil is filled into the sleeve of the sleeve bearing assembly, and the shaft of the rotor assembly is inserted to make a motor sub-assembly. In the condition of the motor sub-assembly, the stopper is secured to the rotor hub. Then, the stopper is in a state of being able to engage the projection disposed at the outer periphery of the top end of the sleeve from thereunder. After that, the sleeve is inserted into the cylindrical portion of the housing of the stator assembly, thereby completing the assembling procedure.
Next, the rotary-shaft type fluid bearing motor disclosed in Japanese Laid-open Patent H11-55900 is explained in the following.
In this prior art example, a hub fixed by a method of press-fitting to a rotary shaft or the like is provided with a stop member made from a magnetic material. Further, an attracting magnet is fixed to the stop member, which is opposed to a core of a coil assembly.
The bearing provided with a herringbone groove is a hydrodynamic bearing which supports the rotary shaft so as to be rotatable in a radial direction, and a thrust plate supports the rotary shaft in an axial direction.
In this configuration, even when a shock or vibration is applied to the motor, the rotary body is prevented from floating due to the attractive force generated between the attracting magnet and the coil assembly. On the other hand, even in case of excessive shocks, the rotary body is prevented from slipping off because it comes in slide contact with the bearing when moving in a thrust direction.
Next, the rotary-shaft type fluid bearing motor disclosed in Japanese Laid-open Patent 2000-50567 is explained in the following.
In this prior art example, a rotor hub is provided with a stop plate for preventing the rotor hub from slipping off. Also, a shaft is secured at the center of the rotor hub, and a drive magnet is secured at the outer periphery, thereby configuring a rotor section.
The shaft is rotatably inserted into the inner bore of a sleeve having first and second cylindrical portions provided with herringbone grooves at the inner periphery thereof. And, a lubricating fluid is filled in the clearance between the shaft and the sleeve, thereby configuring a radial hydrodynamic bearing. Also, one end of the shaft is spherically shaped, and a pivot bearing is formed by the spherical shape and a thrust plate. And, a lubricating fluid is filled in the pivot bearing clearance, thereby configuring a thrust pivot bearing.
The method of assembling in the prior art example is explained in the following. The thrust plate is caulked and fixed to the sleeve to make a bearing assembly. Subsequently, a specified amount of lubricating oil is applied to the inner periphery of the sleeve of the bearing assembly, and then, the shaft of a hub assembly having a rotor hub with a magnetized drive magnet bonded is inserted therein. A stop plate is fixed to the hub, and the stop plate prevents the bearing assembly from slipping off. A predetermined amount of adhesive is applied to the inner periphery of the internal cylindrical portion of a stator assembly, followed by inserting a sleeve with a rotor hub built in. The stator assembly is such that a coil assembly with a coil wound on a stator core is secured by adhesive in a housing.
In this prior art example, the stop plate is caulked and fixed to the rotor hub. A flange is formed at the end of the sleeve. Due to this configuration, when the rotor hub moves in a thrust direction, the flange stops the stop plate, thereby preventing the rotor hub from slipping off.
In the configuration of the above conventional fluid bearing motor, the fluid bearing motor must be assembled according to the procedure as follows: (i) hydrodynamic lubricant is applied to the fixed side bearing, (ii) the rotary body is inserted into the fixed side bearing to be assembled, (iii) a member having a stopping function is fixed to the rotary body, (iv) the rotary body is assembled in such manner as not to slip off from the fixed side bearing, and (v) after that, the fixed side bearing is secured onto a substrate (or bracket, base member, housing) by press-fitting, bonding or other method.
In case the fluid bearing motor is assembled by such procedure, (i) with hydrodynamic lubricant (or lubricating agent, lubricating oil, lubricating fluid) filled in the assembly of the fixed side bearing and the rotary body, a member having a stopping function is fitted to the rotary body, and the fixed side bearing is secured on a substrate. That is, the assembling procedure includes complicated steps requiring careful handling.
Also, the fixed side bearing and rotary body assembly filled with hydrodynamic lubricant is to be frequently handled during the assembling work. Accordingly, it may give rise to leaking or running of the hydrodynamic lubricant filled. And, it is difficult to retain the specified amount of hydrodynamic lubricant. Further, the fixed side bearing may abut or come into contact with the portion opposed to the fixed side bearing of the rotary body. In that case, there may arise scratches or slight bruises on any one of the fixed side bearing and the portion opposed to the fixed side bearing of the rotary body. As a result, it gives trouble in the finished product after completion of the assembly.
Also, in the conventional shaft-fixed fluid bearing motor, there may arise a problem of leaking or running of the hydrodynamic lubricant during the assembling work or due to excessive shocks or other causes. Consequently, in case the hydrodynamic lubricant sticks to the top surface of the thrust holding plate (or upper counter plate, lower counter plate, cover plate), the hydrodynamic lubricant sticks to the surface of the disk attached to the outer periphery of the rotary body due to the centrifugal force caused by rotation, and it may give damage to the recording medium formed on the surface of the disk.
Further, in the above reference for a rotary-shaft type fluid bearing motor, nothing is mentioned about a cover of a fluid bearing motor or disk drive. For the reduction in thickness of a disk drive, a cover is generally disposed close to a rotary body. In this case, there arises a problem such that when the cover is strained due to an external force applied thereto, it comes in slide contact with the rotary body of the fluid bearing motor located near there, resulting in rotational variation of the fluid bearing motor.