1.  Technical Field
The present invention relates in general to an improved hard disk drive and, in particular, to an improved system, method, and apparatus for attaching the top pole piece of a voice coil motor to the cover of a hard disk drive enclosure. 
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 (DASD) 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 or a mixture of glass and ceramic, and are covered with a magnetic coating.  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 (rpm).  Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile (2.5 and 1.8 inches) and microdrive. 
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 (ABS) 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'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. 
In the hard disk drive enclosure, a common means for joining a top pole piece of the actuator VCM to the drive cover is fasteners such as screws.  Due to tolerance conditions, there can be a gap between the cover and the top pole piece.  Under these conditions, the force applied by the screws distorts the drive cover, which adversely affects the nominal attitude of the actuator mechanism.  Likewise, interference between the cover and top pole also distorts the cover. 
An alternative to screw fasteners is the use of one or more leaf spring(s) 211 (FIGS.  1 and 2) located between the cover 213 and the top pole piece 215 of the VCM 217.  Generally, the leaf spring 211 is a funnel-like design having an open, L-shaped perimeter 212 or upper edge and a thin, zig-zag shaped, lower edge opening 214.  Only the upper edge or perimeter 212 contacts and is rigidly attached (e.g., via adhesive) to the cover 213 with a cantilevered boundary condition.  The funnel like body of spring 211 protrudes downward from cover 213.  The opposite end or lower edge opening 214 of the leaf spring 211 does not contact the cover 213, but instead contacts the upper surface of top pole 215 of the VCM 217.  The spring 211 thereby applies a force against the top pole 215 of the VCM 217. 
This prior art leaf spring 211 provides structural stiffness in the plane of the cover 213 while remaining compliant in a direction that is transverse to the plane of the cover.  This design results in reduced cover distortion for the same tolerance conditions described above.  As depicted in FIGS.  1 and 2, a significant drawback of this design is that the space required for the spring 211 reduces the volume available for the top pole piece 215.  This design also causes a reduction in both magnetic flux capacity and corresponding torque constant of the VCM 217 as it completely overlaps the magnetic transition 218 of magnet 217.  Thus, an improved design for interfacing the VCM top pole piece and the cover of the disk drive enclosure would be desirable.