Swage mounting using surface protrusions

Details Swage mounting using surface protrusions Swage mounting using surface protrusions

2001-12-21

2004-06-22

Klimowicz, William (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

Disk record

C360S244500, C360S266100

Reexamination Certificate

active

06754044

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns swage mounting and swage mounted assemblies, such as swage mounts used to connect components used in an actuator arm assembly for a computer hard disk drive.
2. Description of the Prior Art
Swage mounting is used in a wide variety of fastening applications, particularly where assembly cost and height profile are important considerations. One important use of swage mounting is in the construction of disk drives.
Disk drives are used in a variety of devices such as computers, facsimile machines, copiers and any other equipment where mass digital data storage is desired. Two important and costly sub-assemblies in disk drives are a head gimbal assembly (HGA) and a controller driven actuator assembly, referred to as a head stack assembly (HSA). An HSA comprises one or more HGAs, an actuator body, a coil and a bearing. Included in the HGA is a read/write head that is capable of reading digital information stored on platters in the disk drive. The HSA precisely positions the read/write head vertically adjacent a precise point on the disk drive platter, with the actuator directing the movement of the HGA across the face of the platter. Each HGA includes precision-made components manufactured to exacting standards. Because of the complexity involved in each HGA, manufacturers have found that having the ability to disconnect and reconnect the HGA from the HSA substantially reduces costs should either assembly require rework or replacement.
To facilitate the cost-effective repair and/or replacement of these assemblies, the HGA and HSA are typically connected at a stacked joint defined by the distal end of the pivoting actuator arm and the proximal end of a thin elongated load beam. The opposite end of the load beam supports the read/write head that sweeps across the disk platter in response to an actuator controller. Satisfactory operation of the drive requires the read/write head to be selectively positioned vertically adjacent to selected annular data tracks formed on the platter within response times on the order of milliseconds. Such response involves high levels of acceleration. In the event of the actuator accidentally contacting the crash stop during seek, the acceleration levels can reach levels of several hundred Gs. To determine the torque exerted upon the swage mount connection during a crash stop or seek event, the worst case assumptions are made. A conservative estimate for an HGA mass is 100 mg (only the portion extending from the swage mount), with a centroid located 5.6 mm from the swage mount boss centerline. A nano slider (6 mg) typically is located 18 mm from the boss centerline. Using these assumptions, the torque exerted upon the swage mount is at most 0.0007 N*mm/m/s
2
[0.00171 in-oz/G]. Thus, if a 1000G shock event occurred, the resulting torque exerted on the swage mount would be 1.7 in-oz.
During the hard disk drive assembly process, there are several steps which involve placing the HSA in various fixtures and machines. A lateral force of 100 grams (0.22 lbs) on a load beam at a distance of 15 mm (0.59 inch) from the boss centerline results in a torque of 14.7 N-mm (3.8 in-oz). Therefore, the fastener connecting the actuator arm to the load beam must have the capability to withstand considerable torque, on the order of 4-5 inch-ounces or more.
Disk drive manufacturers continually endeavor to reduce the size of their disk drives to meet market demands for faster drive operating speed and increased storage capacity. To increase storage capacity, additional double-sided platters are vertically stacked with each platter having its own HGA. However, adding platters to a disk drive has the undesirable effects of increasing the vertical profile of the drive, increasing component cost and impairing component reliability. As a result, manufacturers have endeavored to miniaturize existing drive components.
One such method for reducing the overall drive size is to reduce the size of the stacked vertical joint connecting the HGAs to the HSA. For example, in U.S. Pat. No. 5,689,389 (Braunheim '389), the contents of which are incorporated herein by reference as though set forth herein in full, a low profile swage mount fastener is used to connect the load beam of the HGA to the actuator arm of the HSA. Because the swage mount fastener has a low profile, the overall height of the disk drive may be reduced, especially in drives using multiple platters and HGAs. However, a disadvantage of using a low profile swage mount fastener is that as performance demands increase, it provides less torque retention than is required to withstand the force levels imposed on the load beam during drive assembly and during shock events.
In Braunheim '389, the torque retention characteristics of a low profile swage mount fastener were increased by modifying the internal geometry of the swage mount. However, the level of torque retention that can be achieved solely by modifying the swage mount design is limited. Without increased torque retention values, the shock-driven acceleration rate a load beam can withstand is limited, which imposes an upper limit on the robustness of the drive package and handling constraints on the drive assembly processes. Accordingly, there is a shortcoming in the art in the unavailability of a low profile swage mount fastener capable of torque retention values that are significantly higher than have been previously achieved.
Moreover, as a platter is accelerated the read/write heads begin to fly, forming an air bearing between the head and the platter. For optimal performance, fly height above the platter must be controlled very tightly, e.g., to between 0.5 and 2 microinch (&mgr; inch). If the head moves too far away from the platter, drive read/write operations are adversely affected. To accomplish the required control, the load beam portion of the HGA is “pre-loaded,” that is, it is biased toward the platter. In pre-loading, the load beam is curved downwardly, such that the read/write head is biased toward the platter. Pre-loading thus creates a downward force on the head so that during drive operation this downward force balances the air bearing and therefore restrains the head from moving away from the optimal height above the platter. Generally, pre-loading of 20 to 40 mN (2 to 4 grams) of force is sufficient to achieve this result. The goal of pre-loading is to achieve an appropriate balance such that the head is close enough to the disk to be able to accurately read data but not so close that the head physically contacts the disk
A present drawback in using a swage mount fastener to join the HGA to the HSA is that the process of swaging causes “gram change,” i.e., it changes the delicate balance achieved through pre-loading. The effect swaging has on gram change is measured by comparing the pre-swage gram load of the HGA when loaded to operating height versus the post-swage gram load. It has been found that an average gram change of about 20 to 100 milligrams (mg) occurs as a result of the swaging process. Accordingly, it would be desirable to provide a low profile swage mount fastener in which gram change could be reduced while increasing torque retention values.
SUMMARY OF THE INVENTION
The present invention addresses these problems by providing components that are specially adapted for better swage mounting and by providing various techniques that can be used in the manufacture of such components.
Swage Mounting Using Increased Surface Hardness
The present invention addresses the problems in the prior art by providing a swage mounting component that has a hardened surface. In this manner, improved torque retention characteristics often can be achieved. More specifically, this aspect of the invention generally concerns swage mounting and swage mounted assemblies, such as swage mounts used to connect components used in an actuator arm assembly for a computer hard disk drive.
Thus, the invention is directed to a component for use in swage mounting t

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