Abstract:
Actuator arm pivot assemblies used in hard disk drives carry the read/write heads used for data transfer to/from the disk surface. Actuator arm pivot assemblies use pivot cartridges for the pivoting mechanism. Typical pivot cartridges are built on a thin sleeve made out of a stiff material, such as stainless steel. This sleeve is expensive to manufacture relative to other parts of the assembly. Eliminating the sleeve from an actuator arm pivot assembly achieves significant manufacturing cost savings.

Description:
FIELD  
       [0001]     The invention relates to hard disk drives, and more specifically, actuator arm assemblies for hard disk drives.  
       BACKGROUND  
       [0002]     Hard disk drives are used in computers and other electronic devices for nonvolatile memory. A hard disk drive allows fast random access reading and writing of data to nonvolatile memory at a reasonable cost.  
         [0003]     A hard disk drive usually consists of one or more platters coated with a magnetic material that can be polarized in order to store bits of information. A magnetic read/write head, which is attached to an actuator arm, reads and writes information to the disk surface. To access different tracks on the disk surface, the actuator arm pivots to change the radial location of the head relative to the center of the disk. A voice coil motor is commonly used to control the movement of the actuator arm.  
         [0004]     Actuator arm assemblies commonly use pivot cartridge assemblies to allow the actuator arm to pivot relative to the hard drive disk. A pivot cartridge usually consists of a sleeve, usually made of stainless steel, two or more bearings, and a shaft.  
         [0005]      FIG. 1  shows a prior art pivot cartridge  10  and actuator arm  12 . The actuator arm  12  holds the voice coil  14 , which is used for controlling movement. The actuator arm  12  may be attached to the pivot cartridge  10  with an adhesive applied to an inner surface  13  of the actuator arm  12 , with a mechanical fastener such as a screw  20  threaded into the actuator arm  12  at a threaded hole  22 , or with a compression ring (c-ring)  16  and spring washer  18  combination.  
         [0006]      FIG. 2  shows a cross section of a typical prior art pivot cartridge  10 . In this example the actuator arm  12  and pivot cartridge  10  are assembled with a c-ring  16  and spring washer  18 . The pivot cartridge  10  includes a sleeve  30 , an upper bearing  26 , a lower bearing  24 , and a shaft  28 . The shaft  28  has a flange  29  that separates the upper bearing  26  and lower bearing  24 . The bearings  24 ,  26  are usually attached to the sleeve  30  with an adhesive. Typically, a preload force (500 g for example) is applied to the pivot cartridge assembly  10  while the adhesive cures. Adhesives are used, because the relatively high preload force cannot be maintained with other methods such as a frictional or interference fit. A suitable adhesive is an ultraviolet light curing adhesive such as Loctite 648UV.  
         [0007]     The sleeve of a typical pivot cartridge, which may have a wall thickness of less than 1 mm, is very expensive to manufacture. If the sleeve could be eliminated from the actuator arm pivot assembly, the disk drive manufacturing cost would be significantly reduced. Thus, there is a need for a sleeveless actuator arm pivot assembly.  
       SUMMARY  
       [0008]     An actuator arm pivot assembly is described with a shaft, bearings, and an actuator arm. One embodiment comprises a pivot assembly with a rotating shaft. Another embodiment comprises a pivot assembly with a stationary shaft. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]      FIG. 1  shows a prior art actuator arm pivot assembly.  
         [0010]      FIG. 2  shows a prior art cross sectional view of a pivot cartridge.  
         [0011]      FIG. 3  shows a first example of an actuator arm pivot assembly.  
         [0012]      FIG. 4  shows a second example of an actuator arm pivot assembly.  
         [0013]      FIG. 5  shows the pivot assembly of  FIG. 4  with an attached actuator arm. 
     
    
     DESCRIPTION  
       [0014]     The pivot cartridge sleeve commonly used in actuator arm assemblies is usually made of stainless steel and has a wall thickness of less than 1 mm. The very thin wall renders the sleeve difficult to manufacture, increasing the manufacturing expense and resulting in a high part cost. Designing the assembly without a sleeve achieves significant cost savings.  
         [0015]      FIG. 3  shows an example of a sleeveless actuator arm pivot assembly. The shaft  40  has a flange  41  that restrains the lower bearing  44 . The actuator arm  42  is positioned between the upper bearing  46  and the lower bearing  44 . The bearings  44 ,  46  prevent axial movement of the arm  42 . The arm  42  is shaped such that a gap  43  exists between the arm  42  and the shaft  40 . The gap  43  allows the arm  42  to freely rotate around the shaft  40  without contact between the arm  42  and the shaft  40 .  
         [0016]     The assembly shown in  FIG. 3  can be assembled by first placing the lower bearing  44  on the shaft  40 . Next, the actuator arm  42  is placed on the lower bearing  44 . Then the upper bearing  46  is placed on the shaft  40  and in contact with the actuator arm  42 . An adhesive is placed between the shaft  40  and the inner race  54  of the upper bearing  46  either before or after the upper bearing  46  is placed on the shaft  40 . A preload is applied to the inner race  54  of the upper bearing  46  before the adhesive is cured. The preload securely clamps the actuator arm  42  between the lower and upper bearings  44 ,  46 . The preload also stiffens the assembly. Stiffening the assembly is desirable as it increases the dynamic response of the system and leads to faster track seek times. After the adhesive is cured, the preload is removed. An optional threaded hole  45  in the top of the shaft  40  allows the outside cover of the disk drive or other structural part to be secured to the shaft  40 . This may further increase the stiffness of the pivot assembly.  
         [0017]     The actuator arm  42  pivot assembly described above uses a stationary shaft  40  with a rotating actuator arm  42 . It is also possible to build an actuator arm  42  pivot assembly with a rotating shaft  40 .  
         [0018]      FIG. 4  shows a second example of a sleeveless actuator arm pivot assembly without the actuator arm  42  attached. The base  58  has a hole  59  that can receive lower and upper bearings  44 ,  46 . The frame of the disk drive or other structural member may be used as the base  58 . The shaft  40  is held in place by the bearings  44 ,  46  and is allowed to rotate relative to the base  58 . The shaft  40  has a flange  61  that keeps the shaft  40  and bearings  44 ,  46  from moving in the axial direction. A preload on the outer race  52  of the upper bearing  46  is shown.  
         [0019]     The assembly shown in  FIG. 4  can be assembled by first placing the lower bearing  44  in the hole  59 . Next, the shaft  40  is placed in the bore of the lower bearing  44 . Then the upper bearing  46  is placed in the hole  59  and on the shaft  40 . An adhesive is applied to the interface  60  between the hole  59  and the outer race  52  of the upper bearing  46  either before or after the upper bearing  46  is placed on the shaft  40 . A preload is applied while the adhesive cures. After the adhesive is cured, the preload is removed.  
         [0020]      FIG. 5  shows the same sleeveless actuator arm  42  pivot assembly of  FIG. 4  with the actuator arm  42  attached to the shaft  40 . The actuator arm  42  can be attached with an adhesive, a mechanical fastener, or other suitable means.  FIG. 5  shows the actuator arm  42  attached with a screw  62 . Also shown is the disk  64  of the hard disk drive. In this example, the disk  64  overlaps both the outer race  52  of the upper bearing  46  and the outer race  50  of the lower bearing  44 . Overlapping the disk  64  with elements of the pivot assembly leads to a more compact hard disk drive. A more compact hard disk drive is desirable as it requires less space in the end product and allows greater design flexibility.  
         [0021]     The embodiments of  FIGS. 3 and 5  discussed above can have many variations. For example, it might be desirable to use lower and upper bearings  44 ,  46  with different outer diameters. Likewise, it might be desirable to use lower and upper bearings  44 ,  46  with different inner bores. The shaft  40  may have a plurality of flanges or equivalent features to axially place the shaft  40 , bearings  44 ,  46 , and/or actuator arm  42 . The shaft  40  may also have one or more flanges designed to stabilize the actuator arm  42  against the shaft  40 . In addition, the hole  59  in the base  58  shown in  FIGS. 4 and 5  may have multiple bore sizes to accommodate different bearing diameters.  
         [0022]     It should also be apparent that sleeveless pivot assemblies can be constructed with multiple actuator arms for disk drives with multiple platters. Such an assembly might require more than two bearings and more complex profiles for the shaft  40  and/or the hole  59  in the base  58 .  
         [0023]     It will be apparent to one skilled in the art that the described embodiments may be altered in many ways without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their equivalents.