Disc drive protective cover to improve shock robustness

Details Disc drive protective cover to improve shock robustness Disc drive protective cover to improve shock robustness

2001-12-06

2004-05-11

Tupper, Robert S. (Department: 2652)

Dynamic magnetic information storage or retrieval

Record transport with head stationary during transducing

Disk record

Reexamination Certificate

active

06735043

ABSTRACT:

FIELD OF THE INVENTION
This application relates to magnetic disc drives and more particularly to an improved protective cover for a disc drive that improves the ability of the disc drive to withstand strong shocks.
BACKGROUND OF THE INVENTION
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the head over the center of the desired track.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Much of the electronics that are essential to the operation of the disc drive are mounted on a printed circuit board assembly (“PCBA”) that is typically mounted to a bottom surface or base plate of the disc drive. The PCBA includes electrical components that manage the operations of the disc drive. For example, the PCBA includes electrical components that control the speed of the spindle and position of the actuator arms over the discs. Similarly, the PCBA also includes electrical components that interface with the computer's processor.
The PCBA is typically attached to the disc drive base plate in a recessed region formed between two opposing mounting rails that extend from opposite sides of the base plate. The mounting rails extend downward and away from the base plate, and a bottom surface of each mounting rail includes threaded holes to provide for bottom mounting of the disc drive to a support surface (such as a drive bay within a computer). By positioning the PCBA within the recessed region formed between the two mounting rails, the mounting rails protect the PCBA from shocks (i.e., when the disc drive is dropped on a flat surface the mounting rails on either side of the PCBA will prevent the PCBA from contacting the surface).
While the mounting rails protect the PCBA from contacting a flat mounting surface, a majority of the PCBA is exposed between the mounting rails and is susceptible to damage, such as an electrostatic discharge, if a person handling the disc drive should touch a conductive element of the PCBA. In light of this danger, a protective cover may be attached to the disc drive assembly to protect the PCBA from exposure to electrostatic discharge. Such protective covers may comprise a flat metal sheet that fits within the recessed region formed between the two mounting rails to closely cover the PCBA. The protective covers minimize handling damage and reduce the problems associated with installing the disc drive within a computer.
However, when a protective cover over the PCBA is used, the protective cover can vibrate and increase the acoustic emissions from the disc drive. One way to reduce acoustic emissions from the protective cover was proposed by Bernett in the pending parent application entitled “Damped Protective Cover to Improve Disc Drive Acoustics,” Ser. No. 09/535,091, filed Mar. 24, 2000. The Bernett application discloses a constrain layer that is secured to a surface of the PCBA protective cover. The constrain layer includes a damping member for damping the vibrations of the protective cover.
While the protective cover guards the PCBA against electrostatic discharges, and the constrain layer reduces the acoustic noise generated by the protective cover, neither the protective cover nor the constrain layer help to protect the internal disc drive components from physical shocks. This is due to the fact that the mounting rails extend below the level of the protective cover so that a bottom surface of the mounting rails form a mounting plane for making flush contact with a mounting surface. Thus, because both the PCBA and the protective cover are recessed between the mounting rails, the protective cover provides no mechanical shock protection when the disc drive is dropped on its base plate (i.e., when it is dropped on the mounting rails). Such impacts may be experienced by the disc drive during transport of the drive (such as by accidentally dropping the drive prior to installing the drive within a computer), as well as during industry standard “topple drop” tests. Rather than providing shock protection, the mounting rails impact the surface and transmit substantially the full force of the shock wave through the base plate to the internal components of the disc drive. The transmission of these large forces can cause the disc drive to fail, such as when the drive heads lift off the surface of the disc and crash back against the disc (the “head slap” phenomenon). Head slaps can damage the heads themselves as well as the surface of the disc, and can create debris within the disc drive that may ultimately lead to a head “crash.” Similarly, where the disc drive employs a ramp for parking the heads when the drive is not energized, large impact forces can damage (e.g., bend) the suspensions which connect the heads to the actuator arms, thereby rendering the head non-operational.
Previous attempts to cushion the drive from external shocks have included adding bumpers or cushions to the base plate and mounting rails of the disc drive. However, such bumpers/cushions do not provide an optimal solution because (1) the bumpers constitute additional parts and therefore raise the cost and complexity of manufacturing the disc drive; and (2) the bumpers may interfere with the smooth bottom plane formed by the mounting rails, thereby making it difficult to effectively bottom mount the disc drive.
Accordingly, there is a need for improving the shock robustness of a disc drive without adding additional components such as bumpers. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
The present invention relates to a disc drive having a shock protection assembly that reduces the shock force applied to internal disc drive components when the disc drive is subjected to a shock force from beneath the disc drive, such as during transport of the disc drive prior to assembly of the disc drive within a computer.
In accordance with one embodiment of the present invention, a disc drive includes a top cover, a base plate, and a printed circuit board assembly mounted to the base plate between two mounting rails which extend downward from a bottom surface of the base plate. The disc drive includes a protective cover mounted to the base plate to cover a majority of the printed circuit board assembly. The protective cover extends a predetermined distance below the mounting rails to shield the mounting rails and the base plate from contact during a shock event. In one embodiment of the invention, the predetermined distance is approximately one millimeter. In a further embodiment of the invention, a shock damper is positioned between the protective cover and the printed circuit board assembly. The shock damper may comprise a layer of energy absorbing foam which extends bet

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