Flutter-free laminar flow suspension for a disk drive

Details Flutter-free laminar flow suspension for a disk drive Flutter-free laminar flow suspension for a disk drive

2002-04-29

2004-06-15

Renner, Craig A. (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

Disk record

Reexamination Certificate

active

06751065

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved suspension for a head suspension assembly to be used in dynamic storage devices or rigid disk drives. More specifically, this invention is directed to certain improvements in the suspension achieved by applying aerodynamic shaping to its side edges to minimize radial motion of the read/write transducer due to flutter-induced dynamics of the suspension assembly that result from air turbulence.
2. Background Information
Suspension assemblies for supporting a slider over a rotating disk in a magnetic data storage device are in widespread use and are well known. Such suspension assemblies typically include a suspension supported at one end by an actuator arm and having a flexure or gimbal at its other end. A slider having a read/write transducer is mounted to the flexure. In operation, the rotating disk creates an air bearing on which the slider floats. The air bearing is defined by etching features on the slider surface closest to the disk. The suspension provides a spring force, typically about three grams, to counteract the force generated by the air bearing, and to position the slider at the proper “fly height” from the disk surface. The flexure is sufficiently compliant to allow the slider to pitch and roll in response to fluctuations in the air bearing created by variations in the surface of the rotating disk. In this manner, the slider is supported and can be positioned over the disk by an actuator assembly in the drive to access or create information on the disk.
The suspension is a cantilever beam that acts as a stiff spring to counteract the force of the air bearing. It is typically fabricated from a flat sheet of resilient metal stock, preferably stainless steel, to minimize size and mass. When designing a suspension, finite element modeling tools are used. The finite element model considers the suspension as a collection of interconnected mechanical elements with known properties. Modern finite element models provide stiffness, damping, resonant frequency and modes of vibration and allow a designer to accurately shape a suspension to achieve the requirements suitable for a given slider design. These requirements include the z-stiffness (i.e., stiffness in the direction perpendicular to the disk surface), resonant frequencies, modes of vibration and allowable dimensions in what to fit between the disks in a disk stack.
The suspensions in suspension assemblies are often provided with stiffening structures or other means for controlling certain required mechanical properties, such as z-stiffness and the resonance frequencies of the suspension. Typically, stiffening rails or flanges are provided at the longitudinal edges of the suspension, such as by bending the edges out of the plane of the suspension. Such edge stiffening rails provide rigidity to the length of the suspension between a substantially resilient spring region of the suspension that is adjacent to the end at which it is attached to the actuator arm of the disk drive, and the other end of the suspension which supports the slider in a read/write position relative to the associated disk. Greater height of the edge rails generally results in increased rigidity. The height of such edge stiffening rails also affects the resonance frequencies of the suspension. It is important to design the geometries and features of such suspensions so that they either possess resonance frequencies that are sufficiently high so as to be out of the range of vibration frequencies that may be experienced in particular disk drives or the like or to minimize the gain caused by any such resonance frequency.
Another manner of increasing rigidity is to simply form the suspensions from thicker materials. However, increased thicknesses also undesirably result in increased spring constants. Increased thicknesses also increase the mass of the suspension, which generally has a negative effect on resonance frequencies and slows the response time for disk access. Rails are advantageous in that the mechanical properties of load beams can be controlled without negative effects on the spring constant and with less mass.
However, a serious disadvantage of side rails, with their flat sides, is that they create turbulence in the airflow over the suspension in the vicinity of the disk spinning at high rpm. Such turbulence is detrimental to the performance of a disk drive because it causes unsteady forces that act on the suspension, causing it to “flutter.” This fluttering increases the incidence of non-repeatable track misregistration, thereby causing read/write errors and hence performance degradation in the disk drives.
The flow of a viscous fluid, such as air, may be classified as laminar or turbulent on the basis of the internal flow structure. In laminar flow, the flow structure is characterized as by smooth motion in laminae or layers. Each layer glides smoothly over the adjacent layer, and there is no macroscopic mixing of adjacent fluid layers. Turbulent flow, on the other hand, is characterized by random three-dimensional flow of fluid particles, causing an exchange of momentum from one portion of the fluid to another. If one were to measure the velocity at a point along the direction of flow in a pipe for both laminar and turbulent flow with the same average flow rate, velocity in the laminar flow case would remain constant with time. By contrast, the instantaneous velocity for the turbulent flow would exhibit random fluctuations about the average flow velocity. For a body immersed in the turbulent flow, these random fluctuations in flow can excite different modes of vibration. In the case of a head suspension for a disk drive, the unsteady forces caused by turbulent airflow causes flutter that produces random track misregistration.
SUMMARY OF THE INVENTION
It is, therefore, a principle object of this invention to provide a flutter-free laminar flow suspension for a disk drive.
It is another object of the invention to provide a flutter-free laminar flow suspension for a disk drive that solves the above-mentioned problems.
These and other objects of the present invention are accomplished by the flutter-free laminar flow suspension for a disk drive disclosed herein.
In an exemplary aspect of the invention, a head suspension assembly for a disk drive is comprised of an actuator arm, a suspension connected at its first end to the actuator arm, and a flexure disposed at the second end of the suspension for supporting a slider with a magnetic head. The suspension has a rigid region between the first and second ends, the rigid region having top and bottom surfaces and side edges. In the rigid region, the side edges are formed into longitudinal stiffeners having aerodynamic cross-sections. The aerodynamic cross-sections cause transverse airflow across the top and bottom surfaces of the rigid region to be laminar and substantially free of turbulence.
In another aspect of the invention, the suspension is manufactured from a generally flat sheet of resilient spring material, preferably stainless steel, by shaping a suspension blank having first and second ends, and a rigid region between the first and second ends, the rigid region having top and bottom surfaces and side edges. The side edges of the rigid region are formed into longitudinal stiffeners having aerodynamic cross-sections. The first end of the suspension blank is configured to connect to an actuator arm, and the second end is configured to accommodate a flexure for supporting a slider with a magnetic head.
In another aspect of the invention, stiffeners with aerodynamic cross-sections are formed at the side edges of the suspension by bending the side edges of the metal suspension blank at an angle, as in a conventional suspension, and then forming an aerodynamic fairing of a moldable material over the bent side edges.
In yet another aspect of the invention, the head suspension assembly including the inventive suspension comprises part of a data storage device that also includes a rotating rigid

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