Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-05-25
2003-12-02
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S069000, C360S075000
Reexamination Certificate
active
06657811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile device having a disk drive that has a reduced battery drain in performing a track seeking operation when operating in a mobile environment.
2. Description of the Related Art
Hard disk drives store large volumes of data on one or more disks mounted on a spindle assembly. The spindle assembly includes a spindle motor for rotating the disks at a nominal angular velocity. Disk drives employ a disk control system for interfacing with a host (e.g., a computer) to control the reading and writing of data on a disk. Each disk includes up to two disk surfaces which are capable of storing data. On each disk surface, user data is stored in concentric circular tracks between an outside diameter and an inside diameter of the disk. Servo systems are employed to maintain alignment of a transducer head with a desired target data track (termed “track following”) for reading and writing user data on the disk surface within desired control parameters.
Embedded servo systems store servo data on the same disk surface as user data to provide control signals and information employed in the operation of the servo system. User data on the disk surface is divided into groups of data sectors. Embedded servo information is recorded in servo sectors placed in arcuate, radially continuous narrow wedges between the groups of data sectors. In this regard, servo sectors are commonly referred to as “servo wedges.” For example, a concentric data track may typically include 120 equally spaced servo wedges with data regions (i.e., a region typically containing 3-6 data sectors and up to 2 partial data sectors) located between adjacent pairs of servo wedges.
Each servo wedge includes fields containing track identification used in track seeking operations and tracking information used in track following operations. For example, the track identification information may include track number and/or address and wedge number, and the tracking information may include automatic gain control (AGC) and phase lock oscillator information (PLO), timing information (e.g., a servo sync word) and servo burst information for positioning a transducer head over the disk surface. The fields are defined by transitions written on the disk surface in patterns readable by the servo system. During execution of a command to read or write data to a target data sector on the disk surface, servo information is sampled as the servo wedges pass under the associated transducer head. The rate at which servo information is sampled, termed “servo sampling rate,” is therefore determined by the number of wedges per track and the angular velocity of the disk.
Disk drive design engineers strive to optimize designs at a servo sampling rate which enables reliable transducer head positioning by avoiding resonances from actuator mechanics, providing adequate servo system phase margins, and detecting shock events. A further constraint on optimization of servo sampling rate is a tradeoff between angular velocity of the disk and the number of wedges per track. Since the wedges are embedded in the data track, some capacity which could be available for user data is consumed, therefore it is desirable to achieve an efficient surface format by only including a sufficient number of wedges per track necessary to meet the optimum servo sampling rate for a given angular velocity.
The process of moving a head from a current track position to a desired or target track position is known as a “seek.” The disk drive includes a servo system that is utilized both to seek to a selected target track and thereafter follow the target track on the disk. A seek to a selected target track is commonly made in accordance with a profile of command effort to the actuator for a respective seek distance, which is stored in memory and accessible by the servo system controller.
The seek profile can be described in terms of current draw, velocity, position or cumulative power consumption. A seek profile (described in terms of velocity) can include three components: an acceleration profile, an optional coast interval, and a deceleration profile. The acceleration profile, typically set to the maximum acceleration permitted by the hardware, involves the initial portion of the seek when the actuator is gaining speed. A coast interval may be included during which the velocity remains substantially constant. The deceleration profile ends with both acceleration and velocity close to zero as the head approaches the target track.
In
FIGS. 2-7
, exemplary idealized current, cumulative power consumption and velocity seek profiles for two seek operations for a given distance are shown. In
FIGS. 2-4
, current, cumulative power and velocity profiles graphically illustrate a first seek operation. In
FIG. 4
, the actuator is commanded to accelerate at time T
0
. This acceleration is maintained until the velocity of the actuator reaches a peak value VEL
PK
. This occurs at time T
SWITCH
. The actuator is then commanded to decelerate, until time T
END
, at which time the deceleration and velocity are brought back to zero, and the head is positioned at the target track. In
FIG. 2
, the corresponding current expended to achieve the velocity profile shown in
FIG. 4
is displayed.
FIG. 3
shows the power consumed in expending the current as shown in FIG.
2
.
In
FIGS. 5-7
, current, cumulative power consumption and velocity profiles graphically illustrate another seek operation in which a coast period is used. As illustrated, the actuator is commanded to accelerate at time T
0
. This acceleration is held until the actuator reaches maximum velocity VEL
PK
at time T
M
, where T
M
is the length of time required to reach maximum velocity. In this example, the maximum velocity VEL
PK
is held (in a “coast” mode) until time T
N
, at which time the actuator is commanded to decelerate so that the velocity decreases to zero at time T
END
.
The velocity profiles illustrated in
FIGS. 4 and 7
are idealized profiles in which the head velocity reaches zero at time T
END
. It is understood in the art that many variables, including resonant modes of the actuator mechanics and stored energy in the actuator mechanics, prevent a precise correction of actuator velocity which would result in the head landing exactly on track at the conclusion of the seek. These variables may cause the head to overshoot the target track, requiring an extended settling period to position the head within an acceptable range of the target track center.
Disk drives have been designed to operate in a mobile environment. For example, a lap-top computer can be taken from the office or home to a remote location. Because the remote location may or may not have an external power source (e.g., line current), the mobile device is provided with an internal source of power such as, for example, a battery. As used herein, a “battery” refers to any of a number of sources of D.C. electrical energy which convert chemical energy, nuclear energy, solar energy, thermal energy, or the like, into electrical energy. Unlike external power sources, batteries have a limited amount of available energy, which needs to be conserved in order to extend the operating time of a mobile device between recharging or replacement of batteries. One typical example of an internal power source is a conventional rechargeable battery, such as a lithium-ion battery.
As shown in
FIGS. 2 and 5
, the servo system draws a significant amount of the available current in seeking target tracks. This results in power consumption that accumulates and can eventually drain the battery. As shown in
FIGS. 3 and 6
, power is consumed for both acceleration and deceleration operations.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a method of performing a seek operation in a disk drive connectable to a mobile device that operates in a mobile environment using battery power and that operates in a docked environment using an external source of power. The disk drive has a spindle moto
Hudspeth David
Knobbe Martens Olson & Bear LLP
Shara, Esq. Milad G.
Tzeng Fred F.
Western Digital Technologies Inc.
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