Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-04-16
2004-03-09
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S078090, C360S078120
Reexamination Certificate
active
06704157
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to data storage device actuators. More particularly, the invention relates to a circuit and method for passive damping of resonance frequency vibrations in data storage device actuators.
BACKGROUND OF THE INVENTION
Rotating disc magnetic recording systems typically employ magnetic head transducers which glide over the magnetic disc media on a cushion of air. The mounting or support structure which carries the transducers are termed “sliders.” Sliders have air-bearing surfaces that are propelled off the surface of moving media by boundary air which moves with the media disc. The air-bearing surface of a slider is aerodynamically designed to glide on the boundary air due to a pattern of raised rails and recesses which establish the “fly height” of the slider. Read/write transducers are mounted on the rear side of the slider, with the reader sensor and writer gap at the air-bearing surface, facing the moving media.
A slider assembly typically includes a ceramic slider and associated read/write heads, a support flexure arm, interconnection wires between the heads and external signaling devices, and any associated mounting hardware. The slider assembly is mounted on an arm which is movable over the surface of a rotating magnetic disc to position the slider adjacent selected tracks on the disc. Disc drives usually employ multiple discs which rotate together, spaced apart from one another on a single spindle. One slider assembly is provided for each magnetic recording surface in a disc drive.
In magnetic disc drive data storage devices, digital data are written to and read from a thin layer of magnetizable material on a surface of one or more rotating discs. Write and read operations are performed through write and read transducers. The slider and transducers are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. When the read transducer is a magnetoresistive (MR) type sensor, the combination of the slider and the transducer are frequently referred to as a MR head. The head is selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface (ABS). As the disc rotates, the disc drags air beneath the ABS, which develops a lifting force that causes the head to lift and fly above the disc surface.
The storage capacity of magnetic disc drive data storage devices continues to increase rapidly. One way in which the storage capacity can be increased is to add more tracks, i.e., by making each track narrower. As the tracks become more narrow and the space between adjacent tracks decreases, the performance demands placed on the actuator to accurately follow a particular track increases. Unfortunately, the tracking ability of the actuator is affected by a number of factors, one of which is resonance.
Most structures have at least one resonance frequency. A structure that receives a resonant frequency as an input can oscillate at a significant amplitude. Slider assemblies and the arms on which they are mounted are not immune to this phenomenon, as slider assemblies are known to resonate at their natural frequencies. The support flexure arm, or suspension, on which the slider is mounted provides the flexibility necessary for the slider body to move vertically in relation to the disc surface. Unfortunately, the support flexure arm also provides a source of vibration as this suspension can oscillate.
Moreover, a given slider assembly that is actively involved in reading and writing can be adversely affected by vibrations in another assembly that is not actively reading and writing. These vibrations degrade the ability of the actuator to follow a particular track on the disc and thus impairs the ability of the head to read to the disc and read from the disc.
In particular, a single actuator arm typically carries two suspensions. One suspension carries a slider or head that reads and writes on the disc above the actuator arm while the other suspension carries a slider or head that reads and writes on the disc below the actuator arm. Only one of the pair of suspensions are actively tracking (and reading and writing) at a time. However, vibrations within a non-actively tracking suspension can negatively impact on the actively tracking suspension.
Thus, damping treatments of one form or another are typically applied. A previous attempt to resolve resonance vibration has been to add a mechanical damper. For instance, a viscoelastic member can be placed on a suspension in order to provide some level of damping. This is illustrated, for example, in U.S. Pat. No. 4,760,478. Alternatively, the particular suspension can be made from materials having improved damping characteristics, as described in U.S. Pat. No. 4,991,045. U.S. Pat. No. 5,909,342 employs particularly designed flexible printed circuits to provide damping.
Unfortunately, mechanical solutions are not without problems. Typically, mechanical damping requires additional components, which translates into greater mass and greater assembly complexity. Moreover, mechanical damping solutions generally require a significant surface area in order to be effective. This has become more of a problem as disc drive actuator systems have become increasingly smaller.
Thus, another possible solution is to actively compensate for excessive vibrations by using a closed loop servo control algorithm. This is described, for example, in U.S. Pat. Nos. 4,414,497; 4,724,370; and 5,079,653. While active servo control such as this is indeed useful in reducing vibration magnitude, there are limitations. For example, in order to provide control over a wide range of frequencies, it is often times not practical to implement an algorithm specifically directed to reducing vibrations at a single frequency. Moreover, with active control, damping is limited to structures being actively controlled.
Piezoelectric materials have been used in other industries for their useful properties. In particular, a piezoelectric material will produce a current in response to a strain and will conversely strain in response to a current. For example, U.S. Pat. No. 5,783,898 describes the combination of a piezoelectric material with a shunt circuit for controlling vibrations in aircraft and the like. U.S. Pat. No. 5,315,203 discloses the use of opposing piezoelectric materials suitable for various large structures.
Thus, a need remains for improved methods of damping vibrations in disc drive components such as slider assemblies and actuators. A need remains for improved methods of controlling resonance frequency vibrations in disc drive components such as slider assemblies and actuators.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a suspension assembly that includes an upper suspension and a lower suspension that is arranged in parallel with the upper suspension. A piezoelectric structure is configured in conjunction with one of the upper suspension and the lower suspension and a damping circuit is electrically coupled to the piezoelectric structure. The piezoelectric structure generates an electrical current in response to a vibration within the piezoelectric structure. This electrical current is dissipated as heat by passing through the damping circuit that becomes at least substantially resistive at the vibration frequency.
According to another aspect of the present invention, there is provided a suspension assembly that includes energizing means that generate an electrical current in response to a resonant frequency vibration within the energizing means and dissipation means that dissipates energy in the form of heat at the natural resonance frequency of the energizing means.
In accordance with yet another aspect of the present invention, there is provided a method o
Himes Adam Karl
Qualey David Gordon
Sluzewski David Allen
Wright John
Merchant & Gould P.C.
Seagate Technology LLC
Sniezek Andrew L.
Wong K.
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