Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-02-23
2004-01-06
Faber, Alan T (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S060000
Reexamination Certificate
active
06674589
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of mass storage devices. More particularly, this invention relates to a method of screening disc drives for various harmonic frequencies.
BACKGROUND OF THE INVENTION
One key component of any computer system is a device 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 an information storage disc that is rotated, an actuator that moves a transducer head 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 head 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 disc drive. Servo feedback information is used to accurately locate the transducer head. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
Controlling the movement of the actuator and attached transducing heads is achieved with a closed loop servo system. U.S. Pat. No. 5,262,907 issued to Duffy et al., and assigned to the assignee of the present invention details an example of such a closed loop servo system. In such a system, position or servo information is prerecorded on at least one surface of one of the discs. The servo system can be either a “dedicated” servo system, in which one entire disc surface in a disc stack is prerecorded with the servo information and a dedicated servo head is used to constantly read the servo information, or an “embedded” servo system, in which servo information is interleaved with user data and intermittently read by the same heads used to read and write the user data.
With either a dedicated or embedded servo system, it is common that the servo circuitry produce a servo position error signal (PES) which is indicative of the position of the head relative to the center of a track. The identity of the particular track, as well as other information relating to the circumferential position of the head on the track, is included, along with other information, in the prerecorded servo information. Thus, when the heads are following a desired track, the PES is essentially at a zero value. The PES is fed back to circuitry used to control current through the coil of the actuator. Any tendency of the heads to deviate from true track center causes the PES to change from its zero value. The PES is a bipolar analog signal, meaning that deviation of the head position away from track center in a first direction will produce a PES of a first polarity, while movement of the heads off track center in the opposite direction will produce an PES of the opposite polarity, and the greater the distance of the head from track center, the greater the magnitude of the PES signal. It should be noted that the PES signal relates to each track centerline, and, as such, when the actuator is seeking from one track to another, the PES signal switches from maximum offset value from a first track in a first direction to maximum offset value from a second track in the opposite direction as the moving head passes the midpoint between the first and second tracks.
In the manufacture of disc drives, it is not unusual for tens of thousands of disc drive units to be fabricated daily. With such high numbers of disc drives being made, it is apparent that a certain number of units will fail to meet the design specifications, due to faulty components, improper assembly, contamination, and other elements familiar to those of skill in the art. While every effort is made by disc drive manufacturers to minimize these defective units and assembly errors, a small percentage of defective units will occur. When the defect is introduced into the unit at an early stage in the manufacturing process, the fault may not be detected until a much later stage of the process. Such a delay in the detection of defective assemblies can result in a significant amount of labor costs when taken over the large numbers of units being manufactured.
It has been found that several mechanical defects that can commonly be introduced into the assembly of a disc drive can be closel
Chen YangQuan
Ding MingZhong
Min ShuangQuan
Ooi KianKeong
Yeo Ricky Wei Watt
Faber Alan T
McCarthy Mitchell K.
Seagate Technology LLC
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