Data storage device operated for reduced sliding contact

Details Data storage device operated for reduced sliding contact Data storage device operated for reduced sliding contact

2001-07-31

2004-03-30

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S031000, C360S053000, C360S073030

Reexamination Certificate

active

06714377

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of mass storage devices. More particularly, this invention relates to loading and unloading sliders in a data storage device.
BACKGROUND OF THE INVENTION
One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disc in a transducing relationship with the disc. The transducer can be used to read information representing data from the disc or write information representing data to the disc. When the disc is operating, the disc is usually spinning at relatively high revolutions per minute (“RPM”). These days common rotational speeds are 7200 RPM. Rotational speeds in high performance disc drives are as high as 15,000 RPM. Higher rotational speeds are contemplated for the future. These high rotational speeds place the small ceramic block in high air speeds. The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disc. The slider has an air bearing surface (“ABS”) which includes rails and a cavity between the rails. The air bearing surface is that portion of the slider that is nearest the disc as the disc drive is operating. 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 depression in the air bearing surface produces a negative pressure area at the depression. The negative pressure or suction counteracts the pressure produced at the rails. The different forces produced counteract and ultimately fly over the surface of the disc at a particular fly height. The fly height is the thickness of the air lubrication film or the distance between the disc surface and the head. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation.
The best performance of the disc drive results when the ceramic block is flown as closely to the surface of the disc as possible. Today's small ceramic block or slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the small ceramic block and the disc is very small. Currently “fly” heights are about 1-2 microinches or less. In some disc drives, the ceramic block does not fly on a cushion of air but rather passes through a layer of lubricant on the disc. A flexure is attached to the load spring and to the slider. The flexure allows the slider to pitch and roll so that the slider can accommodate various differences in tolerance and remain in close proximity to the disc.
Information representative of data is stored on the surface of the memory disc. Disc drive systems read and write information stored on tracks on memory discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the memory disc, read and write information on the memory discs when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disc. The transducer is also said to be moved to a target track. As the memory 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 memory disc. Similarly, reading data on a memory disc is accomplished by positioning the read/write head above a target track and reading the stored material on the memory 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 drive. 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.
One of the most critical times during the operation of a disc drive occurs just before the disc drive shuts down or during the initial moment when the disc drive starts. When shutdown occurs, the small ceramic block or slider is typically flying over the disc at a very low height. In the past, the small block or slider was moved to a non-data area of the disc where it literally landed and skidded to a stop. Problems arise in such a system. Such a system is adequate for disc drives that had textured disc surfaces and which rotated at less than 7200 RPM. To improve magnetic performance, discs now are formed with a smooth surface. To improve access times, disc stacks are now rotated at speeds of 15,000 RPM in a high performance disc drive. Stiction, which is static friction, occurs between the air bearing surface of the slider and the smooth disc surface. Forces from stiction, in some instances, can be high enough to separate the slider from the suspension. When the disc is rotated at 15,000 RPM, the velocity between the slider and disc is high. At high velocity, the kinetic energy that must be dissipated when a contact between the disc and slider occurs is so high that particle generation is a distinct possibility. Still another problem is that landing a slider on the disc may limit the life of the disc drive. Each time the drive is turned off another contact start stop cycle occurs subjecting the slider to another high impact force which may cause the slider to chip or generate particles. The generated particles could eventually cause a head crash in the disc drive.
To overcome the stiction problem and to provide for a much more rugged design for disc drives used in mobile computers, such as portable computers and notebook computers, disc drive designers began unloading the sliders onto a ramp positioned on the edge of the disc. Disc drives with ramps are well known in the art. Such configurations are exemplified in U.S. Pat. 6,243,222 (“Load/Unload Method for Sliders in a High Speed Disk Drive”) issued Jun. 5, 2001 to Zine Eddine Boutaghou et al., also assigned to Seagate Technology LLC.
Conventionally, a portion of the ramp is positioned over the disc. Before power is actually shut off, the actuator assembly moves the suspension, slider and transducer to a park position on the ramp. Commonly, this procedure is referred to as unloading the heads. Unloading the heads helps to insure that data on the disc is preserved since, at times, unwanted contact between the slider and the disc results in data loss on the disc. When starting up the disc drive, the process is reversed. In other words, the suspension and slider are moved from the ramp onto the surface of the disc and into a transducing position. This is referred to as loading the heads or sliders onto the disc.
Use of a ramp to load and unload the disc overcomes many aspects of the stiction problem. However, during the loading process and the unloading process, it seems that it is fairly common for the slider to contact the disc. In such situations, high friction forces can develop between the head and the disc. The high friction forces can cause slider and media damage. The contact with the disc in the disc stack rotated at 1

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