Patent Document

BACKGROUND OF THE INVENTION 
     (1) Technical Field 
     This invention relates to a pivoting actuator used in a head stack assembly (HSA) for a magnetic disk drive, and more particularly, is concerned with improvements in manufacturing and assembly of actuator parts 
     (2) Description of the Prior Art 
     The following four documents relate to methods dealing with improvements to a head stack assembly. 
     U.S. Pat. No. 5,862,019 issued Jan. 19, 1999 to Larson discloses a disk drive actuator assembly adapted for assembly in one of several configurations from a single line of modular components without a manually supervised aligning step. 
     U.S. Pat. No. 6,091,578 issued Jul. 18, 2000 to Stole. et al. describes disk drive actuator components made of composite material including two layers of fibers orientated in a perpendicular direction relative to each other. 
     U.S. Pat. No. 6,002,551 issued Dec. 14, 1999 to Goss, et al, discloses a suspension attachment technique and apparatus for attaching suspension to an actuator arm in a disk drive. 
     U.S. Pat. No. 5,404,636 issued Apr. 11, 1995 to Stefansky, et al, describes a method for assembling a disk drive actuator by inserting a comb device to obtain proper parallelism between stacked drives. 
     For the past several years, data storage methods has followed a tendency of escalating storage capacity while also shrinking the physical size occupied by its storage capacities. Introduction of ever more powerful computer hardware and software has contributed to increasing market pressures for less expensive, larger capacity and smaller packaging in disk drives. Storage device manufacturers make every effort to achieve any possible incremental cost savings that can be reasonably achieved without loss of technical performance. 
     The parts and assembly costs for a head stack assembly (HSA) in a magnetic disk drive represent a significant portion of the total cost of the drive apparatus.  FIG. 1  illustrates main components of a magnetic disk drive apparatus as conventionally used in present day disk drives. Reference numeral  10  denotes a plurality of magnetic hard disks rotating around an axis  11 , and  12  shows an assembly carriage device for positioning each magnetic head slider on a track of each disk. The assembly carriage device  12  is mainly constituted by a pivoting actuator assembly  14  capable of rotating around an axis  13  and a main actuator coil  15  such as for example a voice coil motor for driving the pivoting actuator assembly  14  to rotate. The HSA includes a carriage  14  that is made by machining a suitable material, or by molding or extrusion. Carriage  14  includes one or more suspensions arms represented by the top most suspension arm  16 . 
     Support sections at one ends of a plurality of suspensions  16  are stacked along the axis  13  are attached to the carriage  14 , and one or two head gimbal assemblies  17  are mounted on a top section at the other end of each suspension arm  16 . Each of the gimbal assemblies  17  has the magnetic head slider mounted at its distal end that the slider opposes to one surface (read and write surface) of each of the magnetic disks  10 . 
     The present invention allows an actuator to be made with fewer parts while reducing the total manufacturing cost by simplifying the assembly operation. Moreover, the present invention reduces tolerances in the actuator assembly while improving drive reliability and robustness. 
     In present hard disk drive designs, typically a head slider, is positioned by a head stack assembly (HSA) over and under magnetic disks to perform reading and writing of information to the disks. The constituent elements of a standard HSA&#39;s include a ball bearing pivot assembly and arms extending across the surfaces of one or more pieces of rotating magnetic media. Typically a head gimbal assembly is positioned at a distal end of each arm. Mounted to the head gimbal is a head slider with a read/write orientation with respect to an associated disk. 
     In present designs, parts are aligned to each other using external tooling and secured in place with threaded fasteners. Using external tooling to align parts necessitates precision grade tolerances with controlled aligning references. Moreover, the threaded fasteners add increased parts and cost to the actuator assembly, while creating excessively constrained conditions that induce distortions and misalignment of significant parts within the assembly. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved method for the manufacture of a head stack assembly. 
     It is another object of the invention is to provide a head stack assembly with fewer and less expensive parts while reducing overall manufacturing cost and increasing performance. 
     It is still another object of the invention to simplify the overall assembly operation of the head stack assembly. 
     It is still another object of the invention to reduce manufacturing tolerances yet improving drive reliability and robustness. 
     It is yet another object of the invention is to provide a head stack assembly that does not add mass to the disk drive system thereby achieving reduction in the access time of the magnetic heads to selected data tracks of the rotating disks. 
     It is still another object of the invention not to introduce foreign material into the disk drive. It will not outgas, corrode, wear, or fall off the suspension. 
     The foregoing objects of the invention are accomplished and the disadvantages of the prior art overcome by the provision of a disk self-fixturing pivoting actuator, or as it is also known as a head stack assembly. 
     A novel application of geometrics, kinematics and semi-kinematic design principles are at the center of the present invention. Applying these principles while integrating parts serve the assembly and improves reliability of the pivoting actuator. The design principles provide the full natural tolerance and constraint balance for the assembly of parts. Parts they produce are easier to make, also, function much better as an assembly with zero-stress location. 
     For little or no additional cost, the sheet metal arm and spacers in an actuator assembly can have features added so that the alignment to each other is controlled by the parts themselves and not by using external tooling. 
     The foregoing, together with other objects features and advantages of this invention, can be better appreciated with reference to the following specification, claims, and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a typical head stack assembly from the prior art. 
         FIG. 2  shows an illustration of a head stack assembly according to the invention. 
         FIG. 3   a  shows a top view of the 2.5 inch head stack assembly according to the invention. 
         FIG. 3   b  shows a cross-section of the pivot bearing assembly, according to the invention. 
         FIG. 3   c  shows a partial cross-sectional side view of a head stack assembly according to the invention. 
         FIG. 4  illustrates a primary spacer used for locating and securing all other components of a head stack assembly according to the invention. 
         FIG. 5  shows a secondary spacer used for securing additional suspension arms according to the invention. 
         FIG. 5   a  is a bottom layout view of two coaxially aligned holes disposed on the bottom surface of the secondary apacer shown in  FIG. 5   
         FIGS. 6 ,  7  and  8  show a top view, a side view, and bottom view, respectively, of a head arm assembly according to the invention 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 2  and  FIG. 3   c  showing an exemplary design of a 2.5 inch, or smaller, head stack assembly  50  manufactured in accordance with this invention. In the embodiment shown, the head stack assembly was designed for a disk drive with two disks. The embodiment further includes head assemblies  51   a ,  51   b ,  51   c  and  51   d  with each suspension  52   a - 52   d  distally carrying thin-film magnetic head elements  59  used to read and write information on both sides of these two disks. The details of the four head arm assemblies are best illustrated in  FIGS. 3   c  and  6 - 8 . Referring now to both  FIGS. 2 and 3   c , a stacked sequence of the above multiplicity of parts are as follows: Starting from the bottom of the head stack assembly  50 , there is head arm assembly  51   d , a primary spacer  53 , two more head arm assemblies  51   c  and  51   b , a secondary spacer  54  and the forth head arm assembly  51   a . The lower primary spacer  53  also incorporates a coil, which, along with a magnetic structure mounted to the drive base-plate (not shown), is used to rotate the actuator and move the heads across the disk surfaces. The arms  51   a - 51   d  and spacers  53 ,  54  are slipped over a flanged bearing housing  57  containing cylindrical ball bearings making up the pivot assembly  56  shown in a cross-sectional view in  FIG. 3   b . A bowed snap ring  58  is placed within a receiving groove located opposite the flanged end of the flanged bearing housing  57 . The above mentioned stacked sequence of parts are fixed firmly in place by the applied clamping force provided by the bowed snap ring  58 . No other fasteners are needed for the actuator assembly. 
     As previously mentioned, the proper application of geometrics, kinematics and semi-kinematics design principles are at the center of the present invention. Applying these principles while integrating parts serve the assembly and improves reliability of the pivoting actuator. The design principles provide the full natural tolerance and constraint balance for the assembly of parts. Parts they produce are easier to make, also, function much better as an assembly with zero-stress location. 
     Referring now to  FIG. 4  showing the primary spacer  53 , and  FIG. 5  showing the secondary spacer  54  are each designed with self-fixturing features. The most critical alignment in a disk drive actuator is accurate and stable azimuth alignment of the various arms and spacers. If the alignment is not accurate the various heads will not all reach the outer and inner radii of the disk surfaces at the same time. This reduces the size of the available recording area on the disks and thereby reduces the maximum amount of data that can be stored by the disk drive. Further, if this alignment is not stable, it is possible that the drive will not be able to read back previously written data, which makes it an unacceptable condition. 
     In a self-fixturing design, the azimuth alignment is created and maintained by features intrinsic to the suspension arms  51   a ,  51   b ,  51   c  and  51   d  and spacers  53 ,  54 .  FIGS. 4  thru  8  illustrate the self-fixturing properties.  FIGS. 4 and 5  show designs of the spacers  53  and  54  with basic self-fixturing features. Preferably, both primary and secondary spacers  53  and  54  respectively, are molded of a rigid plastic which includes, on the primary spacer  53 , an over-mold feature  26  for securing a motor coil element. 
     Applying geometric design and statistical process control, directs the design of the primary spacer  53  as a receiving element for which the other parts, namely, arm assemblies  51   a - 51   d , spacer  54 , and flanged bearing housing  57  cooperate.  FIG. 4  shows the design of the primary spacer  53  as the central building block for the entire head stack assembly  50  in accordance with this invention. Locating pins  21 ,  22 ,  23  and  24  are essential elements in the actuator assembly. Pins  21  and  24 , shown in a partial cut-away, are positioned coaxially, one over the other, as are pins  22  and  23 , as illustrated in  FIG. 4 . 
     In  FIG. 5 , the secondary spacer  54  also receives head arm assemblies. As described earlier, and illustrated in  FIGS. 2 and 3   c , the head stack assembly is designed for a disk drive with two disks. Four head arm assemblies  51   a - 51   d  with attached suspensions  52   a - 52   d  with attached thin-film magnetic head elements  59  used to read and write magnetic information on both sides of these two disks. The perspective view of the head stack assembly in  FIG. 2  best shows the overall design package. The assembly configuration of the four head arm assemblies and associated spacers and cartridge bearing is best illustrated in  FIGS. 3   c ,  4  and  5 . An exemplary sequence starts from the bottom of the head stack assembly  50 . Firstly, head arm assembly  51   d  is inverted and urged onto shorter molded pins  23 ,  24  disposed under the primary spacer  53 , shown in  FIG. 4 . The shorter pins are coaxially in line with the upper pins  21 ,  22 . Secondly, arm  51   c  is urged, right side up, onto the longer molded pins  21 ,  22  disposed on the topside of primary spacer  53 . Thirdly, arm  51   b  is inverted and urged onto the longer molded pins  21 ,  22  on top of arm  51   c  previously assembled onto primary spacer  53 . Right side-side up implies an orientation such that the slider containing the magnetic head element is on the lower face of the head arm assembly. Secondary spacer  54 , refer to  FIG. 5 , is urged onto the upper pins  21 ,  22  of primary spacer  53  over the previously assembled arms  51   c  and  51   b , therein sandwiching the two arms between spacers  53 ,  54 . The slotted hole  32   a  and squared hole  31   a  disposed at the underside of secondary spacer  54  as shown in  FIG. 5   a , are coaxially in line with molded pins  21 ,  22  of primary spacer  53  and the upper and shorter molded pins  31  and  32  of secondary spacer  54 . The combination of slotted hole and square hole along with bearing bore  33 , also shown in  FIG. 5 , provide freedom allowing the head suspension assembly to thermally expand, between holes  32   a  and  32   b  relative to the pivot bearing bore  33 , permitting ease for assembly and disassembly of the head suspension assembly. The head suspension assembly  51   a  is placed right side up and urged onto pins  31  and  32 . 
     In a self-fixturing design, the azimuth alignment is created and maintained by features provided on the suspension arms  51  and spacers  53 ,  54 . Referring now to  FIGS. 3   a ,  3   c  and  6 - 8  showing the design of the suspension arm  51 .  FIG. 3   a  illustrates a top view of the suspension arm having two square stamped alignment holes  63 , and  64 , and one stamped alignment slot  62  in each of the suspension arms. Only one of the square holes  63  is used in combination with the alignment slot  62 . This allows a single production tool to be used for suspension arms designed for both right-side-up and inverted use. Each suspension arm  51   a - 51   d  is located in the X and Y directions by a molded pin on a spacer passing through the alignment hole in the suspension arms. The azimuth alignment of each arm relative to the spacers is controlled by a molded pin on a spacer going through the alignment slot in the suspension arm. In both of these two interfaces there is a small amount of interference between the pins and the corresponding features on the suspensions arms so that the positions of the arms are explicitly set and controlled. 
     During the assembly of the suspension arms, an interference between the holes in suspensions  51  and the locating pins in the primary spacer  53  and secondary spacer  54  requires a force to urge the suspension arm over the pins. In the case of a slot sliding over a pin, the force is greatly reduced because there is only contact between the pins and slot at two linear areas on opposite sides of the pins. To reduce the force required to urge the holes over the pins, square holes are used in the suspension arms instead of round holes, thereby reducing the contact to only four linear areas of contact. In FIGS.  6 , 7  and  8  showing a top view of a typical suspension according to the invention, a side view, and a bottom view respectively. 
     With this combination of geometrics and kinematics and semi-kinematics design principles, all of the suspension arms and both spacers are accurately and securely aligned to each other and the alignment is not dependant on external tooling. Moreover, because of the interference at the interfaces, the azimuth alignment of the various parts is well controlled and will not shift over time. 
     In summary therefore, is a rotary actuator assembly for a 2.5 inch disk drive or smaller. The disk drive having a support base and a pivot bearing assembly. The rotary actuator assembly includes a primary spacer standard having a top surface separated from a bottom surface. The primary spacer standard receives at least one suspension arm assembly standard and one secondary spacer standard. The primary spacer is designed having a semi-kinematic arrangement for controlling azimuth alignment. The primary spacer standard includes a datum hole having a pivot axis, the datum hole receives the pivot bearing assembly. A plurality of locator pins are disposed on the top surface and are coaxially aligned with locator pins on the bottom surface. The locator pins receive suspension arm assemblies and a secondary spacer. Accommodation is made for an included coil assembly. 
     While the invention has been particularly shown and described with reference to the preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the inventions.

Technology Category: g