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Disk Drive Head Suspension System optimized for High Dynamic Performance and Low Inertia

IP.com Disclosure Number: IPCOM000124904D
Publication Date: 2005-May-11
Document File: 4 page(s) / 73K

Publishing Venue

The IP.com Prior Art Database

Abstract

Growing demands to increase capacity in HDDs with each successive generation necessitates a significant improvement in the dynamics of the actuator needed to support high track densities. This article proposes the use of Beryllium for the loadbeam, hinge and mountplate components of the suspension to achieve the required characteristics and highlights its advantages over traditional materials. This makes it an attractive proposition for future suspension designs.

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   Disk Drive Head Suspension System optimized for High Dynamic Performance and Low Inertia

  HDD suspension systems serve as compliant members between the actuator arms and the disk surfaces on which sliders containing the recording heads are mounted. The recording heads fly at a constant height (on the order of nanometers) above the disk surface tracking pre-written servo information. An HDD suspension system maintains a set preload on the slider, and in conjunction with the air bearing, enables the slider to track topological variations of the disk surface.

Modern disk drive suspension systems are configured like flat leaf springs and utilize Stainless Steel for the load beam, hinge and mount-plate components. The ideal suspension system would provide the required compliance for the slider in pitch and roll, but be infinitely stiff otherwise. However, such a suspension is not feasible, and to that extent HDD performance and track density are limited by the finite suspension stiffness. This finite stiffness results in mechanical resonances of the suspension system. The lower the stiffness, the lower the frequencies of the suspension modes, and consequently greater is the difficulty in increasing the servo bandwidth. Low frequency suspension bending modes (typically in the 3-4 KHz range) excited by airflow get further amplified by the servo compensator resulting in higher NRRO. The first torsional mode of the suspension (T1) usually limits the achievable servo bandwidth (in cases where it is lower in frequency than the lateral mode of the suspension). Resonances in the cross-track direction (lateral or sway modes) couple strongly to the coil forces and directly translate to cross-track motion of the head.

Suspension systems also contribute significantly to the overall rotary inertia of a disk drive actuator. The rotary inertia of an HDD actuator directly influences the seek times, and in turn the data through-put, a key customer metric in the industry. Hence, to maximize performance, it is imperative to have an actuator with the lowest inertia. Today, up to 40% of an actuator's inertia can derive from the head-suspension assembly using traditional materials. This inertia contribution only increases in actuators with high head counts.

In summary, all of the above factors severely limit the growth of track density in future generations of disk drives. Hence, an ideal suspension would have very low rotary inertia and possess high stiffness.

Intuitively, one can surmise that a higher suspension stiffness can be obtained by using a thicker structural member. However, this also increases the rotary inertia of the device. In order to improve the dynamic characteristics of the suspension while lowering the inertia simultaneously, materials with a high specific stiffness (modulus/density) are required. Prior art and all suspension systems in use today are constructed of stainless steel flat springs (known as load beams and hinges). What is pro...