Abstract:
A system for preventing the accumulation of excess lubrication in the form of lubricant lines on magnetic media disks for hard disk drives uses a mandrel design that produces negligible surface waves when the disks are dipped in lubricant baths. The mandrel has inverted tear drop shaped supports for the disks. The supports are smaller in overall size than an inner diameter hole formed in the disks and diminish the formation of waves in the lubricant bath.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to hard disk drives and, in particular, to an improved system method, and apparatus for preventing the accumulation of excess lubrication in the form of lubricant lines on magnetic media for hard disk drives. 
     2. Description of the Related Art 
     Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy, glass or a mixture of glass and ceramic, and are covered with a magnetic coating that contains the bit pattern. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute. Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile and micro drive. 
     A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. 
     A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk&#39;s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system. 
     The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track. 
     As the areal density of magnetic media in hard disk drives increases, the thickness of the lubricant used to coat the media must be decreased to avoid adverse effects on the performance of the disk drives. The thickness of media lubricants has been reduced to such a level (e.g., on the order of 10 Å for some applications) that the uniformity of the lubricant layer is a significant issue. 
     One particular concern is the formation of wide lubricant “lines” on disks during the lubricant application process. Lubricant lines can be several angstroms thicker than the overall lubricant coating on the disks. The lubricant lines remain on the disks, even after pad burnishing and temperature and/or humidity treatments. These relatively thick lubricant lines are potentially damaging to the flight characteristics of sliders. In addition, lubricant lines cause head smear/lubricant pick-up on the sliders, thereby reducing their durability. 
     Conventional disk holders produce surface waves in the lubricant bath that cause the lubricant lines to form on the disks. One type of prior art design uses a cover for the bath in an attempt to suppress the magnitude of surface waves. Unfortunately, that design requires precise positioning and careful operation throughout the process, which can cause inadvertent scratches on the disks and give rise to even bigger problems during manufacturing. Although this conventional design is workable, a more effective solution for preventing the formation of lubricant lines on magnetic media would be desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of a system, method, and apparatus for preventing the accumulation of excess lubrication in the form of lubricant lines on magnetic media for hard disk drives are disclosed. The invention provides solutions to problems associated with the prior art by employing a novel mandrel design. The mandrel design produces negligible surface waves in the lubricant bath during the dipping phase of a cassette of magnetic media disks. In one embodiment, the mandrel comprises a plurality of inverted tear drop shaped supports. The supports are smaller in overall size than an inner diameter hole formed in the disks and diminish the formation of waves in the lubricant bath. Compared to prior art solutions, the invention is simple in design, readily implemented, and robust to operate. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic plan view of one embodiment of a disk drive constructed in accordance with the invention; 
         FIG. 2  is an isometric view of one embodiment of a fixture (shown with one media disk) for lubricating media disks for the disk drive of  FIG. 1  and is constructed in accordance with the invention; 
         FIG. 3  is a top view of the fixture of  FIG. 2  and is constructed in accordance with the invention; 
         FIG. 4  is a side view of the fixture of  FIG. 2  and is constructed in accordance with the invention; and 
         FIG. 5  is an end view of the fixture of  FIG. 2  and is constructed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a schematic drawing of one embodiment of an information storage system comprising a magnetic hard disk file or drive  111  for a computer system is shown. Drive  111  has an outer housing or base  113  containing at least one magnetic disk  115 . Disk  115  is rotated by a spindle motor assembly having a central drive hub  117 . An actuator  121  comprises one or more parallel actuator arms  125  in the form of a comb that is pivotally mounted to base  113  about a pivot assembly  123 . A controller  119  is also mounted to base  113  for selectively moving the comb of arms  125  relative to disk  115 . 
     In the embodiment shown, each arm  125  has extending from it at least one cantilevered load beam and suspension  127 . A magnetic read/write transducer or head is mounted on a slider  129  and secured to a flexure that is flexibly mounted to each suspension  127 . The read/write heads magnetically read data from and/or magnetically write data to disk  115 . The level of integration called the head gimbal assembly is the head and the slider  129 , which are mounted on suspension  127 . The slider  129  is usually bonded to the end of suspension  127 . The head is typically formed from ceramic or intermetallic materials and is pre-loaded against the surface of disk  115  by suspension  127 . 
     Suspensions  127  have a spring-like quality which biases or urges the air bearing surface of the slider  129  against the disk  115  to enable the creation of the air bearing film between the slider  129  and disk surface. A voice coil  133  housed within a voice coil motor magnet assembly  134  is also mounted to arms  125  opposite the head gimbal assemblies. Movement of the actuator  121  (indicated by arrow  135 ) by controller  119  moves the head gimbal assemblies radially across tracks on the disk  115  until the heads settle on their respective target tracks. 
     Referring now to  FIGS. 2-5 , representative embodiments of a system, method, and apparatus for preventing the accumulation of excess lubrication in the form of lubricant lines on magnetic media for disk drives are shown. As depicted in  FIG. 2 , the system comprises a reservoir or bath  201  containing a volume of solution or lubricant  203  as is known by those having ordinary skill in the art. For example, the lubricant  203  may comprise a low concentration of lubricant and a volatile solvent that evaporates after the lubricant is applied. 
     One or more media disks  115  (e.g., one shown for simplicity) are located on a fixture  205  adjacent the bath  201 . The fixture  205  is used to support and dip the media disk  115  in the volume of lubricant  203  in the bath  201 . The fixture  205  has a mandrel  207  with an axis  209 . A plurality of partitions or dividers  211  are mounted to the mandrel  207 . The dividers  211  axially abut one another (e.g., in a parallel configuration) to define slots  213  therebetween. Alternatively, the dividers  211  may be formed as a single component that mounts to the mandrel  207 . Each slot  213  is designed to support one of the media disks  115 . Each slot  213  may comprise a circular groove formed between adjacent ones of the dividers  211 . 
     In operation, the disks  115  are retained on the mandrel  207  by the slots  213  between the dividers  211 . The disks  115  are lowered and submerged in the lubricant  203  and then removed therefrom at a constant rate. The lubricant is uniformly distributed over the surfaces of the disks  115 . During the lube dipping process, the disks are fully immersed beneath the surface of the lubricant solution in a deep bath. The disks are then removed from the bath at a selected rate of speed that controls the thickness of the lubricant that remains on the disks. 
     It is the unique designs and shapes of the dividers  211  that prevent the lubricant  203  from forming waves in the bath  201 . In one embodiment ( FIG. 5 ), each divider  211  has an axial cross-sectional shape that resembles an inverted tear drop. 
     Each divider  211  may be provided with an upper end  215 , two side edges  217 , and a lower end  219 , each of which is axially spaced apart from the upper ends  215 , side edges  217  and lower ends  219  of other ones of the dividers  211  as best shown in  FIGS. 3 and 4 . The upper ends  215  and side edges  217  are generally arcuate or circular in shape, while the lower ends  219  are pointed in shape. The upper ends  215  protrude above the mandrel  207  by an upper distance. The side edges  217  protrude laterally from the mandrel  207  by a side distance that is greater than or equal to the upper distance. The lower ends  219  protrude below the mandrel  207  by a lower distance that is greater than the side distance. Bach divider  211  comprises a rounded partition that is curved both axially and radially with respect to the axis  209 . Each rounded partition has a lower end  219  that tapers both axially and radially to a point as shown. The same configuration may be used when the dividers are formed as a single component. 
     In still other embodiments, the shape of the dividers is not limited to inverted tear drop designs. Alternate shapes may be used such as pointed or spiked shapes that significantly diminish or eliminate the agitation of the liquid surface of the lubricant solution when removing the disks from the bath. 
     The invention also comprises an apparatus for forming a lubricant layer on media disks, as described herein, that may be used to function as a component of the overall system. The invention further comprises a method of lubricating media disks. For example, in one embodiment, the method comprises providing a fixture with a mandrel having an axis and dividers mounted to the mandrel, the dividers axially abutting one another to define slots between the dividers; supporting media disks on the fixture such that each slot supports one of the media disks; placing a volume of lubricant in a bath; lowering the media disks with the fixture to dip the media disks in the volume of lubricant; and lifting the media disks out of the volume of lubricant with the fixture such that the dividers reduce a level of agitation of the a surface of the volume of lubricant. 
     The method also may comprise providing each divider with an axial cross-sectional shape that resembles an inverted tear drop; or providing each divider with an upper end, two side edges, and a lower end, each of which is axially spaced apart from the upper ends, side edges and lower ends of other ones of the dividers. As shown and described herein, the upper ends and side edges are generally arcuate, and the lower ends are pointed. Alternatively, the upper ends protrude above the mandrel by an upper distance, the side edges protrude laterally from the mandrel by a side distance that is greater than or equal to the upper distance, and the lower ends protrude below the mandrel by a lower distance that is greater than the side distance. The method also may comprise providing each slot as a circular groove formed between adjacent ones of the dividers; or providing each divider as a rounded partition that is curved both axially and radially with respect to the axis, and each rounded partition has a lower end that tapers both axially and radially to a point. 
     To test the invention, a transparent lubricant draining bath was constructed, and a video microscope was set up for direct observation of the lubricant “dipping” process. Microscopic video footage of the process clearly demonstrated that excess lubricant lines are caused by the surface waves of the liquid lubricant level as it drops suddenly from the bottom edge of the disk holder. Video microscopic observation of the process clearly indicates that a fixture constructed in accordance with the invention diminishes the surface waves in the lubricant bath. Optical surface analyzer imaging of disks demonstrates that the invention effectively prevents the formation of lubricant lines on disks. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.