Dynamic disc pack balance correction

Details Dynamic disc pack balance correction Dynamic disc pack balance correction

2000-06-09

2002-07-16

Hall, Carl E. (Department: 3729)

Metal working

Method of mechanical manufacture

Electrical device making

C029S596000, C073S460000, C073S462000

Reexamination Certificate

active

06418612

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of disc drive data storage devices, and more particularly, but not by way of limitation, to an automated assembly process of a disc drive assembly which includes a dynamic balance correction station.
BACKGROUND
Modern hard disc drives are commonly used in a multitude of computer environments, ranging from super computers through notebook computers, to store large amounts of data in a form that can be made readily available to a user. Typically, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc is a data recording surface divided into a series of generally concentric recording tracks radially spaced across a band having an inner diameter and an outer diameter. Extending around the discs, the data tracks store data within the radial extent of the tracks on the disc surfaces in the form of magnetic flux transitions induced by an array of transducers, otherwise commonly called read/write heads. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
The read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the read/write head transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
As is known in the art, each read/write head is mounted to a rotary actuator arm and is selectively positionable by the actuator arm over a selected data track of the disc to either read data from or write data to the selected data track. The read/write head includes a slider assembly having an air-bearing surface that causes the read/write head to fly above the disc surface. The air bearing is developed as a result of load forces applied to the read/write head by a load arm interacting with air currents that are produced by rotation of the disc.
Typically, a plurality of open-center discs and spacer rings are alternately stacked on the hub of a spindle motor. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common centerline. Movement of the discs and spacer rings is typically constrained by placing the stack under a compressive load and maintaining the load by means of a clamp ring. Collectively the discs, spacer rings, clamp ring and spindle motor hub define a disc pack envelope or disc pack. The read/write heads mounted on a complementary stack of actuator arms, which compose an actuator assembly, commonly called an “E-block assembly,” accesses the surfaces of the stacked discs of the disc pack. The E-block assembly generally includes a precision component, known to those skilled in the art as an E-block, which provides a mounting for the voice coil, the load arms for the read/write heads, the flex circuit assembly, the cartridge bearing assembly and the read/write head wires.
The read/write head wires, which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a flex circuit connector. The connector in turn is mounted to a flex circuit mounting bracket, and the mounting bracket is mounted to a disc drive basedeck. External to the basedeck the flex circuit connector is secured to a printed circuit board assembly (PCB). For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled METHOD OF ASSEMBLING A DISC DRIVE ACTUATOR issued Apr. 11, 1995 to Stefansky et al., assigned to the assignee of the present invention.
The head-disc assembly (HDA) of a disc drive is typically assembled in a clean room environment. The need for maintaining a clean room environment (free of contaminants of 0.3 micron and larger) is to ensure the head-disc interface remains unencumbered and damage free. The slightest damage to the surface of a disc or read/write head can result in a catastrophic failure of the disc drive. The primary causes of catastrophic failure, particularly read/write head crashes (a non-recoverable, catastrophic failure of the disc drive) are generally characterized as contamination, exposure to mechanically induced shock, and non-shock induced damage. The source of non-shock induced damage is typically traced to the assembly process, and generally stems from handling damage sustained by the disc drive during the assembly process.
Several factors that bear particularly on the problem of assembly process induced damage are the physical size of the disc drive, the spacing of the components, the recording densities sought to be achieved and the level of precision to be maintained during the assembly process. The high levels of precision required by the assembly process are necessary to attain the operational tolerances required by the disc drive. The rigorous operational tolerances are in response to market demands that have driven the need to decrease the physical size of disc drive while simultaneously increasing disc drive storage capacity and performance characteristics. Demands on disc drive mechanical components and assembly procedures have become increasingly more critical in order to support capability and size in the face of these new market demands. Part-to-part variation in critical functional attributes in the magnitude of a micro-inch can result in disc drive failures. Additionally, as disc drive designs continue to decrease in size, smaller read/write heads, thinner substrates, longer and thinner actuator arms, and thinner gimbal assemblies will continue to be incorporated into the drives, significantly increasing the need to improve the assembly processes to protect the read/write heads and discs from damage resulting from incidental contact between mating components. The aforementioned factors resultingly increase the difficulty of assembling disc drives. As the assembly process becomes more difficult, the need to invent new tools, methods, and control systems to deal with the emerging complexities pose unique problems in need of solutions.
Coupled with the size and performance improvement demands are further market requirements for ever-increasing fault free performance. In response to demands for enhanced reliability, some solutions have begun to emerge. Some disc drives have incorporated the use of ramp load technology. By incorporating ramp load technology, the need to physically merge the E-block assembly with the disc pack during the assembly process is circumvented. The read/write heads are not loaded onto the media until after completion of assembly and the drives are spun-up for the first time. The improved performance is obtained by eliminating read/write head induced media damage, basically by insuring an air bearing is present prior to the read/write heads being loaded to the discs.
Ramp load technology is generally limited to smaller disc drive systems, namely sub 3.5 inch form factors, because those disc drives have relatively few discs so tolerance stack-ups do not become a major factor in the assembly process. Increases in disc diameter, coupled with increasing the number of discs in the disc pack, heighten the demands of maintaining the dimensional, mechanical and operational integrity between the E-block and the disc pack. Tolerance stack-ups become very critical in the assembly process and conformation of dimensional attributes of the disc pack and the E-block assembly must be made prior to any attempts in merging the two. Dependence on ramp load technology as the means to accomplish the head-disc merge for larger diameter, multiple surface disc packs would permit a number of E-block to disc pack interface mismatches to escape the process, resulting in sub-optimal performance or even failure or the product. Ramp load technology fails to provide the precision and repeatability required by larger and more complex disc drives.
The progression of continually decreasing disc thickness and disc spacing, together with increasing

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