Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2001-07-11
2004-06-08
Ometz, David L. (Department: 2653)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
Reexamination Certificate
active
06747840
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of data-storage devices. More particularly, this invention relates to a method and apparatus for reducing acoustic noise radiated by a disc drive.
BACKGROUND OF THE INVENTION
Devices that store data are key components of any computer system. Computer systems have many different devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, and circuitry that is used to write and/or read data to and from the disc via the transducer. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil (or “write head”) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or “read head”) that detects changes in the magnetic field along the tracks for reading data.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (“ABS”) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
An operating disc drive can emit relatively large amounts of acoustic noise generated by vibrations of the disc drive enclosure caused by the pressure from inside air, disturbed by the rotating discs. The spindle and actuator movements create forces that act on the structure of the disc drive. When the forces are applied to the device enclosure, the forces are converted into displacements which in turn create pressure waves in the surrounding air which are perceived as acoustic noise to the human ear.
The actuator assembly moves in response to energizing a voice coil motor to move the actuator assembly around a pivot axis, thereby swinging each of the arms associated with the actuator assembly, the load springs, and associated read/write head over the associated disc surface. When moved in this manner during normal operation, the assembled load springs and associated read/write head tend to vibrate at some frequencies. The spindle motor rapidly spinning the discs contributes additional vibration. Vibration from the spindle motor and movement of the actuator assembly may be transmitted to the disc drive housing through the pivot and spindle journals. The resulting vibration in the housing causes radiation of acoustic noise, especially from the cover. Such acoustic noise may be annoying and may suggest poor quality to the user. There are also standards for acoustic noise that are required by many manufacturers.
The device enclosure actually acts like a radiating surface for the internal forces created by the spindle and actuator movement. The dynamics of the device enclosure, such as the natural modes of vibration, can amplify for the forces generated inside the drive. A frequency chart of disc drive sound power indicates that the highest level of drive noise emission is in the frequency band resulting from the first cover resonance. In this frequency band, the cover loses its efficiency to provide transmission losses to counter act the noise produced by the rotating discs. Moreover, the cover response to forces produced by the voice coil motor (VCM), the actuators, and the spindle motor at the first cover resonance is maximal which results in additional increase in the cover vibration and sound radiation in the above referenced frequency band.
In practice, the first cover resonance takes place in the frequency range of 1000-1500 Hz and its width is about 50-100 Hz depending on the specific design of a particular disc drive. The existing VCM actuators have the first acoustically significant resonance (resonance of arms, coils and yokes) in the vicinity of the first cover resonance. More importantly, if actuator resonant frequencies coincide with the cover resonant frequencies, the additive effect will increase cover vibration and the noise radiated from the disc drive.
As a result, acoustic noise emanating from a disc drive is a critical performance factor that is usually tightly specified to be below a maximum level. As part of the quality assurances practices when manufacturing disc drives, the drives are tested in an acoustic chamber to determine the amount of noise emanating from the device. Drives that emit noise above a maximum threshold need to be reworked to be in compliance with the requirements.
Government agencies throughout the world are now requiring that the decibel level of average sound energy emanating from office equipment be substantially reduced. Computer manufacturers are also placing acoustic emission standards on disc drive manufacturers. Manufacturers of disc drives have also long recognized that certain improvements for data storage performance in disc drives, namely, to increase disc rotation velocity, contribute to unwanted acoustic noise. There is a marked decrease in human sensitivity to acoustic noise below about 200 Hz and above about 6000 Hz. Thus, it is cl
Daniel Matthew
Kovinskaya Svetlana I.
Beacham C R
Buenzow Jennifer M.
Ometz David L.
Seagate Technology LLC
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