Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-06-30
2003-07-15
Hudspeth, David (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06594102
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a disk drive in which a disk is used as data-recording medium and the head writes data on the disk and read data from the disk. More particularly, the invention relates to a disk drive in which the head is retracted to a retract position.
A hard disk drive has a head and a head-retracting mechanism. The head is a slider having a read/write element, designed to write data on a disk and read data therefrom. The head-retracting mechanism retracts the head to a prescribed retract position when the disk is stopped and the head stops writing data on or reading data from the disk.
In a CSS (Contact Start and Stop) disk drive, the retract position is provided in the CSS area located at the innermost track of the disk. Thus, the head is retracted to the CSS area when the disk is stopped. The head, thus retracted, contacts the CSS area and remains in standby state. The head slides on the surface of the disk when the spindle motor provided in the disk drive starts rotating the disk and also when the spindle motor stops rotating the disk. The head may damage the disk, leaving “scars” or the like on the surface of the disk. Therefore, the CSS area cannot be used as a data area, and is provided in a retract zone (also known as “dedicated landing zone”), which is distinct from the data zone. When the CSS disk drive is turned on, the spindle motor starts rotating the disk. As the spindle motor rotates the disk at high speed, an air bearing develops, which makes the head float above the disk. The head is moved from the retract zone to the data zone and positioned at a target position (i.e., a target track which the head will access to).
When the CSS disk drive is turned off or when a host system gives a command to the CSS disk drive to stop the spindle motor, the head is retracted to the CSS area and the spindle motor is stopped thereafter. When the head reaches the CSS area, the actuator supporting the head abuts on a stopper. The head is thereby prevented from jumping out of the CSS area. A voice coil motor (VCM) drives the actuator in the radial direction of the disk, moving the head in the same direction. The VCM so operates as it is supplied with a drive current from a VCM driver, which is controlled by the microprocessor (CPU) incorporated in the CSS disk drive.
The supply of power to the CSS disk drive may be abruptly stopped while the head is writing data on the disk or reading data therefrom. If this happens, the head must be retracted to the CSS area before the spindle motor stops. Unless the head is retracted so, it will collides with the disk when the disk creases to rotate while the head is floating above the data zone of the disk. Once the supply of power to the CSS disk drive is stopped, the VCM driver no longer supplies a drive current to the VCM. The actuator can not move the head at all.
In view of this, a new type of an HDD (Hard Disk Drive) has been developed. This HDD incorporates a reserve power supply having a capacitor (or a rechargeable battery). The capacitor is charged while the drive is being driven with the power supply (main power supply). When the main power supply is interrupted, power is supplied from the reserve power supply to the VCM, whereby the head is retraced. Another type of a disk drive has been developed, which has no reserve power supplies and in which the back electromotive force (EMF) generated as the spindle motor is driven is used to retract, the head.
Disk drives, known as “head loading/unloading type,” have been developed. Each disk drive of this type has a head loading/unloading mechanism. The head loading/unloading mechanism retracts the head to the retract position, unloading the head, whenever the disk stops rotating. At the retract position, a ramp is provided and supports the suspension of the actuator. When the disk acquires a normal rotation speed after it has started rotating, the head loading/unloading mechanism moves over the disk, loading the head. The mechanism prevents the head from contacting the disk, thus maintaining the surface smoothness of the disk and reducing the flying height of the head. This helps enhance the recording density of the disk.
As shown in
FIG. 2
, the head loading/unloading mechanism has a ramp (retract position)
14
located at the circumference of the disk
11
. To unload the head, the actuator
13
is driven, moving the suspension
131
. The head (slider)
12
supported by the suspension
131
is thereby moved to the ramp
14
. As a result, the distal end of the suspension
131
, to which a tab (not shown) is attached, then slides onto the inclined surface
141
of the ramp
14
. The head
12
is thereby lifted above the surface of the disk
11
. A stopper (not shown) stops the actuator
13
at a prescribed position outside the circumference of the disk
11
.
During the normal operation of the disk drive, that is, while the disk drive is being supplied with power, the CPU incorporated in the disk drive controls, with high precision, the speed with which the actuator
13
is moved to unload the head
12
. This is necessary, because if the speed is too high, the impact the suspension
131
exerts on the ramp
14
when it contacts the inclined surface
141
will increase, inevitably increasing the possibility that the disk
11
or the head
12
, or both, are damaged.
The supply of power to the disk drive may be interrupted before the head
12
is unloaded (or retracted). If this happens, the disk
12
is stopped in the same way as in the CSS disk drive described above. Consequently, the head
12
collides with the disk
11
. In order to prevent the collision, the disk drive of head loading/unloading type has a reserve power supply having a capacitor, just like the CSS disk drive. When the supply of power from the main power supply to the disk drive is interrupted, power is supplied from the reserve power supply to the VCM, which drives the actuator
13
, thereby unloading. (retracting) the head
12
.
With either the CSS disk drive or the head loading/unloading disk drive, it is possible to retract the head at an abrupt interruption of the supply of power, by means of the reserve power supply (including a back EME). Either disk drive is, however, disadvantageous in the following respects.
In a CSS disk drive containing a disk having a diameter of 2.5 inches, the reserve power supply supplies power to the VCM when the supply of power from the main power supply interrupted, as has been mentioned above. The head is thereby retracted, thanks to the use of the reserve power supply. The time required to retract the head from the data zone of the disk to the CSS area thereof is tens of milliseconds at most, even if the head is located at the outermost track, i.e., the remotest position from the CSS area. While the head is retracted, an almost constant current is supplied to the VCM from the reserve power supply. The value of the current depends on the capacitance of the reserve power supply. Driven by the VCM, the actuator moves the head. The speed at which the head is moved is proportional to the time required to retract the head from the data zone to the CSS area and is proportional to the square root of the distance the head is moved.
Assume that the CSS area, the innermost track and the outermost track have a radius of 15 mm, a radium of 16 mm and a radius of 31 mm, respectively. Then, the speed with which the actuator collides with the stopper when the head is retracted to the CSS area from the innermost track is about four times the speed with which the actuator collides with the stopper when the heat is retracted to the CSS area from the innermost track. Nonetheless, the speed with which the actuator collides with the stopper can be reduced to decrease the impact, because the actuator is driven with a relatively small current in the CSS disk drive. This speed should be of such a value as will cause the actuator to generate a force greater than the offset force of the FPC (Flexible Printed Circuit) board, which has terminals, connected to the head
Kanda Hiroyuki
Kusumoto Tatsuharu
Osafune Koji
Gray Cary Ware & Freidenrich LLP
Hudspeth David
Kabushiki Kaisha Toshiba
Slavitt Mitchell
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