Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the record
Reexamination Certificate
2000-06-15
2004-05-25
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the record
Reexamination Certificate
active
06741414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rotating media storage systems. More particularly, the present invention relates to a method and system for joint spindle speed and head position control to reduce rotational latency and seek/settle time of the rotating media storage system, and thus increase the overall performance of the system.
2. Description of Related Art
Fast and accurate access of stored data while minimizing power consumption, noise, heat generation, and mechanical disturbances are some of the most important considerations when designing and optimizing rotating media storage systems. In addition, there is an ever-present desire to decrease the average time required to access any needed data on the rotating medium (for example, a disk) while maintaining reasonable costs for performing the access.
For current rotating media storage devices such as computer hard disks, compact disks (CDs and CD-ROMs), digital video disks (DVDs), magneto-optical disks, etc., the location of the stored data is generally tracked by two indicators: “track” and “sector”. The first indicator, “track”, refers to what track the data is located on, and the second indicator, “sector”, refers to the radial position on the track where the data is located (i.e., the sector/radial position is between 0 and 360 degrees).
In general, there are two types of data storage/data access on rotating media. The first is structured/ordered data storage/access and the second is random data storage/access. In structured/ordered data storage/access (for example, streaming video) all rotating media tracks are block-recorded next to each other, and the blocks are accessed in the order in which they are saved, thus making the stored data more compressed and more predictable to find and access. In random data storage/access (for example, transaction data for credit cards) the stored data may consist of numerous individual records located throughout the entire rotating media and accessing those individual records may be done in a random manner and not by adjacent blocks. Locating and randomly accessing such random stored data is more difficult and time-consuming.
Referring to
FIG. 1
, a simplified block diagram of an example rotating media storage device
10
(for example, a computer hard disk drive system) is illustrated. Rotating media storage device
10
includes a disk platter (for use with a disk)
20
and a disk drive read-write head assembly
25
. The disk
20
rotates about a spindle
30
, driven by a spindle motor
35
, as controlled by a spindle motor control system
40
.
Most existing rotating media storage systems, such as the computer hard disk drive shown in
FIG. 1
, have disk platters
20
that rotate (i.e., spin) at a fixed rotational speed (e.g., 5,000 rpm, 7,600 rpm, or 15,000 rpm). The spindle motor control system
40
is a low bandwidth (typically under 10 Hz) control system for maintaining the steady-state rotational speed of the spindle
30
. The speed of revolution of the disk platter is therefore controlled by the spindle motor
35
and spindle motor control system
40
.
The read-write head assembly
25
is attached to an actuator assembly
50
(actuator). In the hard disk drive example, the actuator
50
is usually a radial or voice coil motor (VCM) or in other applications may be a linear (push/pull) motor, etc. The actuator control system
55
is a high bandwidth (e.g., 400 Hz to 900 Hz) control system that seeks a new track
21
rapidly and maintains the head position over the rotating storage media track
21
.
Disk drive interface controller
60
controls the overall operation of the disk drive system and the exchange of data between the disk drive and the host device such as a CPU. Read-write control
65
controls the read and write operations on the disk by the head assembly
25
. Power supply
70
provides the necessary power to drive the disk drive system
10
. In
FIG. 1
, power supply
70
is illustrated as being connected to spindle motor control
40
and actuator control
55
, however, it should be noted that there could be multiple power supplies that are individually coupled to each of the controls and/or the power supply may be part of (or supplied by) the CPU. Other embodiments and variations on the connections of the power supply may also be used.
Limits do exist on how fast the read-write head assembly
25
can physically move from the outermost edge
20
a
of the disk platter
20
all the way to the innermost edge
20
b
of the platter
20
. Furthermore, faster track seeks (i.e., faster movement of the head assembly
25
) can lead to increases in noise generation, mechanical disturbance, power consumption, heat generation, and other conditions that may negatively impact the performance of the rotating media storage system.
Currently, some systems use trajectory optimization to improve the tracking of the head assembly
25
to the desired track. Such trajectory optimizations may be performed by minimizing the arrival time, t
f
, of the head to the desired track over the design trajectory of the actuator, u
Actuator
(t). The trajectory optimization may be formulated as:
x
0
→
min
(
t
f
)
u
Actuator
subject
to
:
l
1
⟨
u
Actuator
⟨
l
2
x
PES
(
t
f
)
=
0
x
.
PES
(
t
f
)
=
0
x
PES
(
t
0
)
=
x
0
x
.
PES
(
t
0
)
=
0
J
2
x
¨
=
u
Actuator
→
u
Actuator
(
t
)
where x
0
is the initial radial position of the head position actuator, x(t) is the radial head position at time t, u
Actuator
are the design variables of the actuator, l
1
<u
Actuator
<l
2
are the constraints on the actuator authority where l
1
and l
2
are the lower and upper limits, respectively, based on the actuator constraints and hardware, x
PES
(t) is the radial head position error and x
PES
(t)=x
Desired
−x(t), x
PES
(t
f
)=0 is the arrival position error, {dot over (x)}
PES
(t
f
)=0 is the arrival velocity error, x
PES
(t
0
)=x
0
is the starting position error, {dot over (x)}
PES
(t
0
)=0 is the starting velocity error, and J
2{umlaut over (x)}=u
Actuator
is the physical equation of motion for radial head position where J
2
is a coefficient of inertia and {umlaut over (x)} is acceleration.
It should be noted that the physical equations of motion given in the formulation above have been simplified for ease of understanding herein. As such, one with ordinary skill in the art would know that the equations of motion given in the formulation above are merely representational and other equations of motion with greater detail and more variables may be used.
This formulation addresses optimal head position (track seek).for constant spindle speed. In actuality the above trajectory optimization does not take into account the spindle speed at all because the spindle speed in this design is not a variable.
The solution to this trajectory optimization problem is the so-called switching function solution (Bryson and Ho, Applied Optimal Control, 1967). An approximation to this switching function is used in some systems and is described by PTOS (Proximate Time Optimal Solution) (See Franklin, Powell, and Workman, Digital Control, 1992, pp 583-584, Chapters 11 and 12). The switching function solution, also known as “bang-bang control”, pushes as fast as it can for half the time and then reverses and pushes in the opposite direction for the remaining half of the time in order to reach a desired location. In other words, in the hard disk drive example, the switching function solution would first determine how long it would take to move the head from the starting position to the desired position (i.e., time period for arrival). Once the time period for arrival is determined, then the switching function solution pushes the actuator with the greatest force possible (given the constraints and conditions of the sy
Boyd Stephen
Erickson Mark
Kanellakopoulos Ioannis
Shah Sunil C.
Blakely Sokoloff Taylor & Zafman LLP.
Hudspeth David
Tokyo Electron Limited
Tzeng Fred F.
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